although i can't understand why in the world you would want him to stop you in the fabric store ( :shock: ) i guess you could try one or more of these tricks:
1) he can't pick out any fabrics for new quilts until he finishes knitting something for you. even "trade". he can pick for 1 quilt for each knitted item AFTER he has completed it.
2) get him started on a fisherman's knit sweater set. go to the store(s) by yourself while he's distracted working on that.
3) he can't pick out any new yarn until you've finished a quilt. (naaaa ... bad idea. too much pressure already to actually finish a quilt. LOL)
4) my personal favorite - as long as you aren't having to switch to eating cat food, shop 'til you drop!!!
LOL