hi,
replacement of the evap is really the only proper way to do this,but i dont recomend you do this repair by yourself unless you are fairly competent and have all the right tools to start with.
there is one other option......depending on how bad the leak is you can get a stop leak kit for a/c systems bit like you put in a leaking radiator and works on same princible.
dont know where you would get one over your way but try an a/c specialist or good auto parts store.
these kits only work on minor leaks and are obviously not a permanent fix, but cheap and worth a go.

steve.