Visiting Tibet from Nepal - need a multiple entry visa.

I'm visiting Tibet in a week on a 9-day tour from Nepal ending in Lhasa. My permit in Tibet is good for 17 days. I want to fly to Vietnam and tour south east Asia for 2 weeks or so before returning to Hong Kong to join a tour through mainland China Ending in Beijing on November 7th.
Would it be easier to just stay in PRC for the two weeks and get a 1 month vist at the expiration of my Tibet permit than to try to get the multiple entry one?
Thanks,
Nathan