three inches is quite a bit. how much does the seat need to come in? it might be too much.
for more info go to ask andy search. ask for "trouser alterations" scroll down to that title.
its pretty far down there dated 7-4-06.
Learn how to sew and do your own tailoring. Practice on a cheap pair of trousers from the local op shop the first couple of times and purchase a good book on the subject eg Reader's Digest Book of Sewing. You'll enjoy tailoring your own trousers, jeans etc as it's not that difficult. I began six years ago because I needed to hem a pair of pants and it's led to me not only tailoring my clothes but producing bushwalking gear such as sleeping bags, tents, packs, rainwear, gaiters etc and learning how to repair sewing machines; none of which is difficult on the old 1959 Necchi sewing machine my mother purchased at a garage sale for $A8.00. Give it a go!