diff --git a/README.md b/README.md
index aa3ed97..75cefb9 100644
--- a/README.md
+++ b/README.md
@@ -31,7 +31,7 @@ Flags:
 
 - `--latest-fork`: Enable the latest fork at startup
 - `--use-reth-for-validation`: Use Reth EL for block validation in mev-boost.
-- `--secondary-el`: Port to use for a secondary el (enables the internal cl-proxy proxy)
+- `--secondary-el`: Host or port to use for a secondary el (enables the internal cl-proxy proxy). Can be a port number (e.g., '8551') in which case the full URL is derived as `http://localhost:<port>` or a complete URL (e.g., `http://remote-host:8551`), use `http://host.docker.internal:<port>` to reach a secondary execution client that runs on your host and not within Docker.
 - `--use-native-reth`: Run the Reth EL binary on the host instead of docker (recommended to bind to the Reth DB)
 - `--use-separate-mev-boost`: Spins a seperate service for mev-boost in addition with mev-boost-relay
 
diff --git a/playground/recipe_l1.go b/playground/recipe_l1.go
index d619d12..a87f097 100644
--- a/playground/recipe_l1.go
+++ b/playground/recipe_l1.go
@@ -2,6 +2,7 @@ package playground
 
 import (
 	"fmt"
+	"regexp"
 
 	flag "github.com/spf13/pflag"
 )
@@ -15,9 +16,12 @@ type L1Recipe struct {
 	// useRethForValidation signals mev-boost to use the Reth EL node for block validation
 	useRethForValidation bool
 
-	// secondaryELPort enables the use of a secondary EL connected to the validator beacon node
-	// It is enabled through the use of the cl-proxy service
-	secondaryELPort uint64
+	// secondaryEL enables the use of a secondary EL connected to the validator beacon node
+	// It is enabled through the use of the cl-proxy service. If the input is a plain number, it is assumed
+	// to be a port number and the secondary EL is assumed to be running on localhost at that port.
+	// Otherwise, it is assumed to be a full address (e.g http://some-el:8551) where to reach the secondary EL,
+	// use http://host.docker.internal:<port> to reach the host machine from within docker.
+	secondaryEL string
 
 	// if useNativeReth is set to true, the Reth EL execution client for the validator beacon node
 	// will run on the host machine. This is useful if you want to bind to the Reth database and you
@@ -39,7 +43,7 @@ func (l *L1Recipe) Flags() *flag.FlagSet {
 	flags := flag.NewFlagSet("l1", flag.ContinueOnError)
 	flags.BoolVar(&l.latestFork, "latest-fork", false, "use the latest fork")
 	flags.BoolVar(&l.useRethForValidation, "use-reth-for-validation", false, "use reth for validation")
-	flags.Uint64Var(&l.secondaryELPort, "secondary-el", 0, "port to use for the secondary builder")
+	flags.StringVar(&l.secondaryEL, "secondary-el", "", "Address or port to use for the secondary EL (execution layer); Can be a port number (e.g., '8551') in which case the full URL is derived as `http://localhost:<port>` or a complete URL (e.g., `http://docker-container-name:8551`), use `http://host.docker.internal:<port>` to reach a secondary execution client that runs on your host and not within Docker.")
 	flags.BoolVar(&l.useNativeReth, "use-native-reth", false, "use the native reth binary")
 	flags.BoolVar(&l.useSeparateMevBoost, "use-separate-mev-boost", false, "use separate mev-boost and mev-boost-relay services")
 	return flags
@@ -52,6 +56,8 @@ func (l *L1Recipe) Artifacts() *ArtifactsBuilder {
 	return builder
 }
 
+var looksLikePortRegex = regexp.MustCompile(`^\d{2,5}$`)
+
 func (l *L1Recipe) Apply(svcManager *Manifest) {
 	svcManager.AddService(&RethEL{
 		UseRethForValidation: l.useRethForValidation,
@@ -59,13 +65,18 @@ func (l *L1Recipe) Apply(svcManager *Manifest) {
 	})
 
 	var elService string
-	if l.secondaryELPort != 0 {
+	if l.secondaryEL != "" {
+		address := l.secondaryEL
+		if looksLikePortRegex.MatchString(l.secondaryEL) {
+			address = fmt.Sprintf("http://localhost:%s", l.secondaryEL)
+		}
+
 		// we are going to use the cl-proxy service to connect the beacon node to two builders
 		// one the 'el' builder and another one the remote one
 		elService = "cl-proxy"
 		svcManager.AddService(&ClProxy{
 			PrimaryBuilder:   "el",
-			SecondaryBuilder: fmt.Sprintf("http://localhost:%d", l.secondaryELPort),
+			SecondaryBuilder: address,
 		})
 	} else {
 		elService = "el"