I have finally punted this into the contribs repo. PPTP needs to die and this does work as a replacement on most phones with no additional software.
The contrib works, but sure it could do with some refinement.
Note with this version you should be able to disable pptp, but use the server manager to enable or disable user access as you did with pptpd. So once setup it should be easy to control.
There is a wiki page
https://wiki.contribs.org/Smeserver-libreswan-xl2tpd but it could probably do with some tidying up.
There should be a new section in bugzilla to report bugs on the contrib. Please ask questions here or report bugs there.
Please ask if you have questions.