Hi Jarryd - I just bought a spare lens cap, cut a hole in it and securely taped a piece of Baader AstroSolar Safety Film on the inside.
I got the cap from a box of spares at a camera shop. You need a cap that's the right fit (obviously!) and that isn't too complex a design on the inside - ie no impediment to cutting a hole, and if you cut a hole the tabs still work. I have a Canon DSLR but the lens I use for solar is a Sigma 55-200mm. The filter works really well and is nice & secure.
Good luck!
Cheers -