Recently some evaluation users were asking whether Gerber files are required for fundamental heat spreading studies in a printed board. No, they aren't! TRM allows to created traces, planes and circles in the graphics window of the component table (youtube: Current Carring Capacity and IPC-2221) . Add the proper material and vertical position within the layer stack and all is done. Adding heat sources or currents is the same procedure. Drill areas can be blocks penetrating several layers parametrized by their effective conductivity. I did some experiments imitating the JEDEC-51 2s2ps test boards and it works (with assumptions).