Custom claims in userinfo but not in ID token

[per]

I’d like to include custom claims in the userinfo response. I have succeeded by creating a rule that adds a custom namespaced claim to the ID token. However, the claim also appears in the ID token (obviously). Is there a way to avoid that, i.e. keep the ID token “slim”? My client code doesn’t always need these custom claims, so it’d be nice to only have them in the userinfo response.