There are several of us on ECF who have been looking at a work around for the ego tank system on non-Ego batteries. The battery extender being spoken about here is 7/8 inch and leaves quite a gap between the battery housing and the Ego tank atomizer...which allows too much air flow and thusly for it to work exactly how it was intended--not to mention that is doesn't look aesthetically pleasing.
I did find a 510 to 510 adaptor from avidvapor.com that I ordered but it is only 1/4 inch. The clearance that you'll need between the battery housing and for the ego atomizer to sit properly is 7/16 inch( but this may vary depending upon which mod you have).
Right now it looks like the best option is going with a 510-901 to 901-510 adaptor which I have on order. If you go to this link on ECF (super-T forum) you will see our discussion and pictures of how this looks on a P-18:
http://www.e-cigarette-forum.com/forum/super-t-manufacturing/107626-receiving-line-p18.html. The discussion and pictures start on 1/26/11 on this thread. Also, there are some other threads in different forums on ECF discussing this situation previously, but this is the most up-to-date.
By the way, this discussion talks about me getting an infinity mod, I have since cancelled that order and have a Provari on the way.
Hope this makes sense...I've only had a few sips of coffee so far.