Why don't you just grab the sources, unpack them and compile them. All you have to do is set a configure parameter. So if you want to install in the /bla/php directory you say
Code:
./configure --prefix=/bla/php
Of course you should also add other configurations parameters that suit your needs. Hope this helps. Cheers
PS
This doesn't imply that your apache can work with this other php instalation. Using the same method you can also install a second apache server
PPS
This is a general method, and it is not quite clean, nor is it dependency aware. But it will work on any distro