The striker will go straight into the Pirates' squad for Saturday's crucial game against Walsall.
"Obviously we have been looking round for a bigger striker and Rene fits that bill," boss Dave Penney told the club's official website.
"He's got the physical presence that we have been looking for as a different option for Jo (Kuffour) and Will (Hoskins) and it just gives me a different option up front."
Howe was happy to join Rovers in an bid to play more first-team football.
"I'm happy to come here. I just needed to get away from Peterborough and play some games," he said.