here's my best recommendation.

talk to Henry Menzies <[email protected]> of Menzies Tours in Corozal. if he doesn't answer, then get ahold of Judy Wilson <[email protected]>, and have her get ahold of him. Henry is new-ish with email and sometimes takes a bit to respond. but he's awesome and can totally give you all the possibilities.

Here's about his biz:
Menzies Tours, based in Corozal Town in northern Belize, has a wealth of services to offer. They arrange tours and do transfers in Belize and Mexico. At the Caribbean Village in South Corozal, they have a restaurant, Hailey's, and they will cater a special meal for a group if you like. There is also a fully equipped RV park, with a dumping station, electricity, and water.
http://www.corozal.bz/tours/

here's their transfers page, if they come and get you:
http://www.corozal.bz/tours/transfers.htm