I actually bypass the transfer of lava to the overworld.
I put thermal generators directly in the Nether next to my lava Pump (Buildcraft pump powered by 4 redstone engines).
The thermal generators feed into an MFE, that charges energy crystals and ships them to back to the overworld once fully charged via an enderchest.
This is achieved with two filters (RP2) and a timer. Simply place fully discharged energy crystals into overworld enderchest and wait a bit, then get a fully charged energy crystal in a few seconds.
I'll have to talk to my friend about this... how would I discharge crystals into machines though?