I think you could.
I was making a homemade 150w HMI once, and I put a 5" fresnel lens on a little cheapo PAR can. Worked like a charm. Of course it's a fixed-focus fresnel, but that was fine in my application.
I'd say the biggest thing would be to make sure it's not all sealed up too tight, so that plenty of air can still get to the globe to avoid overheating.
T2
__________________________________
Todd Terry
Creative Director
Fantastic Plastic Entertainment, Inc.
fantasticplastic.com