Recently I bought a machine from Mega Electronics for inserting tiny rivets into 0.7mm diameter drill-holes in home-made PCBs. The result is a fairly low-profile via, with decent electrical conductivity even without soldering. I'm hoping they will be sufficiently flush with the surface of the board to allow me to place vias under the 0.5mm lead-pitch TQFP packages used for Xilinx FPGAs:
