The blocks are already supported in plain C mode as long as you enable the Clang extension. You just use, for example, block_Copy(aBlock) instead of [aBlock copy]. Apple framed it as a C feature in its proposal for standardization (because Objective-C doesn't have a real standard AFAIK).
Seriously, though, is there a reason the Objective C blocks wouldn't work in C, just substituting functions for methods?