fcgi modules

I’m moving servers.
New server has CentOs7.1 and fresh build of Virtualmin Pro.
One of the sites I’m moving over currently runs under mod_php which I don’t want.
The problem is it needs mbstring but this is not showing as a module under PHP in virtualmin when the site is set to fcgi. It does when set to mod_php.

If I want to add a module to php normally I can do like yum install php-mbstring.

How do I do this with fcgi?

I’ve done a bunch of googling which seems to infer I need to recompile fcgi.
No easier way?

If I have to recompile is there a Virtualmin safe method?

TIA