According to sources, Universal will use archival audio of Paul's voice for Fast 7, and merge that with the voices of his brothers Caleb and Cody.
While nothing could ever fill the hole that Paul's death left in the entertainment community, his brothers will apparently be able to fill the gaps in his archival audio for dialogue purposes.
Sources say that the two brothers were tested for audio, and certain words sounded better from Caleb, and others from Cody, so the two will both be assisting in the production to get the dialogue to where it needs to be.
On top of that, it seems that Caleb and Cody have already started working on the flick!
It's really nice that the people behind Fast 7 are including Paul's family. It's so clear how he loved being in that franchise.