Non-polar solvents are simply transparent to microwaves, and you can't to anything to the oven to change that.
Take a look at the table in https://www.thevespiary.org/rhodium/Rhodium/pdf/solvent.miscibility.pdf (https://www.thevespiary.org/rhodium/Rhodium/pdf/solvent.miscibility.pdf)
The "polarity index" is a rough comparative estimate on how effectively different solvents are heated by microwaves. As you can see, Water has an index of 9, while pentane/hexane has a 0. Toluene/Xylene is at a very low ~2.4-2.5.