While maya offsetcurve has function for cutting loop, it doesn’t work with degree 1 curves. My previous attempt has problems determining which loop to discard, now resolved by looking at the overall clockwise/counterclockwise order of the region.
(see http://stackoverflow.com/questions/1165647/how-to-determine-if-a-list-of-polygon-points-are-in-clockwise-order).

Also had a look at http://en.wikipedia.org/wiki/Winding_number, will look into implementing this if there is any problem with the current method.