will work.
just a couple of things to keep in mind
are you using a red or red/orange lux (the lux needs to isolated from the sink, better use Arctic Alumina)
do you think you will ever need to "upgrade" the lux? (may want to use something other then an epoxy so you can remove the lux without damage)
If you're using more than one white Lux, you'll have to isolate the slugs. For a single one, and assuming you're also using the heatsink as negative contact, it doesn't really matter.