maybe something like a tincan would work? I'm not sure on the diameter though, you'd need to measure it.
Do you suspect a boost leak?
Did you ever get the problems with that map sorted?
I have one i bought you can borrow @ cost of post mate? Bought it from Ebay for about £40 delivered IIRc. Handy bit of kit
Someone recently fabricated an S4 pressure tester using a tin of dog food.
Mmmm... meaty!