Thank you for your inquiry.
It is hard to do what you described in fcgi, as the fcgi process is persistent, and it cannot switch to a different user id when a script belong to another user dispatched to this fcgi process. That's why you need to configure a dedicate fcgi PHP handler for each user.
It is possible with our lsapi php implementation, but haven't been implemented.
If you want to setup suexec at per user level, you still have to setup a dedicated fcgi/lsapi PHP application and script handler for each user with LSWS, however, LSWS has vhost template feature which will make configurations for mass hosting less painful. :-)
LSWS can do per user chroot as well, but you have to setup the chroot jail environment for each user manually, it is a pain and no way to automate that.