Yes, I looked into the MLCC option earlier. My primary goal was to be able to power the RFM radio at full tx power for the duration of one message (about 1 second at SF12), to match the link budget calculation (link to separate thread).
0805 MLCCs seems to be the sweet spot. We can then get 100uF in a package that's 0.079"" L x 0.049"" W (2.00mm x 1.25mm) with a height of 0.057"" (1.45mm).
To power the radio for a second I'd need about 0.2F (calculator). 0.2F equals 2,000 x 100uF. Placing 50x40 0805 packages optimally will utilize 62.5x80mm which is about 4x the size of the PCB.
So it seems the MLCC option won't be able to solve the tx power problem. But placing 100x100uF would definitely be possible, and that would give a nice buffer for other things.