Although just another voice, i 3rd the use of portal engine. There are ways if you really need to get into the code behind of a file you can do this even with Portal Engine. There have been previous sites made in aspx vs. portal and it's always a nightmare to work on!
If i may inquire, what will be the specific purpose for using the aspx template? What functionality are you looking for, we may be able to instruct how to do it easily with portal method.