Logic in dynamic environment url

Description

We're currently using GitLab CE with CI and we're loving it (especially the dynamic environments), but I've run into a little problem.

A lot of our branches contain a slash e.g. daniel/feature-x, but the URL for the dynamic environments can't contain a slash in our setup since it has a special meaning in the path. I've tried bash-style substitution, but that does not seem to work.

Maybe there is some clever solution that I hadn't thought of, but I couldn't find anything in the docs.

Our current setup

environment:
    name: review-apps/$CI_BUILD_REF_NAME
    url: https://domain/${CI_BUILD_REF_NAME}

What I tried

environment:
    name: review-apps/$CI_BUILD_REF_NAME
    url: https://domain/${CI_BUILD_REF_NAME/\//-}

Proposal

Either support some style of substitution to allow some logic to be inserted.