I'm having some trouble with the syntax used in the {re.subst,expression}
method. What i want to do is add a prefix to a capture group.

I can make it work like that  /^[0-9]+/prefix$tU/ but this solution is far from perfect since i may not need the entire $tU.

I would like to use it like this  /^[0-9]+/prefix\1/ in order to not limit my regex to Kamailio only.  When i do it like this the regex result is only "prefix".