High power LED on aluminium core PCB
I needed this TO220 to dissipate a lot more than a TO220 can. The limiting factor was the silpad at the back (similar to your case). So I soldered it on a flat piece of copper and mounted that on the heatsink. The much larger silpad area does wonder to heat removal!



Since this is a one-off I suggest doing the same, reflow the LED on a big chunk of copper, and bolt that on the heat sink with thermal grease.