It seems that the purpose of UG heating cables (if one discounts the "warm feet" effect) is to circulate water through/into the substrate. This provides O2, nutrients, etc. to the substrate (laterite, etc.). The only points against a UG filter (reverse or otherwise) is the clogging of the filter with roots and the distribution of fine sediment into the water. Well, how about using that bubble wand stuff? You know, the 3/16" X 12" rod that you pump air through for bubbles? Attach several lengths to some sort of manifold (PVC?), bury it in the substrate, and then pump filtered water through it. I don't think most roots would clog this stuff, and the flow would be gentle enough to not disturb the laterite or whatever in the substrate. The only possible drawback I see is the potential for the bubble wand material to become clogged. But, passing the water through some decent filtration first might keep it in check. If you don't want to pump water through, how about CO2? !
This would at least provide "some" water movement through the substrate. JMTT (Just my tightwad thoughts.)