1. If portability is not a concern, you could probably use assembler to examine the overflow bit directly (probably since it depends on the tools you have available), and do something relevant if you determine that it has been set.

2. Implement the multiplication by hand, i.e. as repetitive addition. E.g. take the largest number, add it to an accumulator the number of times indicated by the smallest number. Before each addition check that the difference between MAXINT (65536 in the case of unsigned short) and the number being added is less than the number being added. If not you will get an overflow, i.e.

if(MAXINT-largeop<largeop)