Arduino Mega: Interrupt not working? Use any pin for interrupt?
You are right when you say "technically they aren't interrupt pins".

The only pins you can use as interrupts are 2, 3, 18, 19, 20 and 21. There is no way of changing that. You can't magic more interrupts out of thin air.

However there is a different interrupt system that may help you out - the pin change interrupts.  These are harder to work with since they are grouped into sets of pins that share the same interrupt, but there are far more pins with this kind of interrupt available. Note that you still have to be careful which pins you choose.

There are a couple of libraries available to help you configure the PCINT registers should you need it.