You can mod the IMS20mm reflectors, and possibly mod the heatsink.
I will be doing both very soon. I have one of modamags new heatsinks (does both tri or quad) for luxeons. I'm going to make it flat to get rid of the centering depressions for the luxeons, and then place the cree's by hand, mark them, then epoxy them.
The reflectors will be drilled out, and shortened to optimal focus. Then attached with glue and possibly a sleve/holder made from PVC pipe or something, since they will be shorter and the lens won't hold them down.
I'm going this route because 1) I have all the parts already, 2) I can't afford the McR19mm version (because of the $18ea reflectors). 3) Hopefully I'll have it built before the 19mm heatsink is out!
I'll post info sometime when I get started on it (shouldn't be too long) about what you gotta do as I go along.