Got a power amp device where it's "foot" pokes through a hole in the PCB and solders to a plate of metal, which in turn is itself soldered to the PCB ground plane & screws to a chassis that doubles as a heatsink.
I've got a replacement power amp FET to solder in there, but need some ideas on how to desolder the old one. The picture below shows my dilemma. The red circle is the thing I need to heat up to get the power FET off (I've already got it's pins off the PCB on the other side... that's no problem). Want to avoid heating the other items in yellow... pretty much everything surrounding the plate I need to heat.
I've tried a SMD hot air reflow to heat the plate, and can't get enough heat quickly enough into it to allow the power FET to come free. I can't get anywhere near enough heat in from the top side of the PCB either, where I'd have to send the heat through the FET body first to get to it's foot.

I'd previously done something similar in another device by resting the plate on an upside down domestic clothes iron to pre-heat the plate, then heated it up just that little bit more with the SMD hot air reflow station to get it off. But that was a carrier PCB with nothing else around it. Can't do that here because of the surrounding components.

Ideas??