Using parameters in http-request set-map filenames

I’m trying to update my haproxy config to allow different map files to be updated using http-request set-map as described in the haproxy blog, Introduction to HAProxy Maps

Instead of hardcoding the map filenames I would like to take them from a URL parameter, because I have several map files and I would rather not create separate acls for each file.

I tried this:

http-request set-map(/etc/haproxy/%[url_param(map)].map) %[url_param(path)] %[url_param(target)] if is_map_update

but that doesn’t result in any updates in the specified map file.

Updating it to hardcode the map filename works:

http-request set-map(/etc/haproxy/debug.map) %[url_param(path)] %[url_param(target)] if is_map_update

Is there a way I can update the rule to specify the filename for the set-map using url parameters?