I will be travelling on a 90 day work visa but need to leave Thailand twice in that time.

Is it possible to get a multiple re-entry permit at BKK, and if not, can I simply get two single re-entry permits, one each time I fly out?

I understand I can go to the 'Immigration 1' office in the city, but this is not logistically as easy as it sounds for me, so would prefer to do it all at the airport if it is possible.

N.B. I have tried to get a multiple entry visa from London but for my purpose of work they only offer single entry at the embassy, which then has to either be converted to multiple in Thailand, or used alongside a re-entry permit.