Unless you have excellent TIG welding skills, heed the above mentioned advice and look for better rims. If you are capable of welding the rims, you will want to cut away all of the rust damaged area around the valve stem hole and weld it up solid, and grind and sand it perfectly smooth. Then you will need to drill a new valve stem hole in another area on the rim.
If the rims are badly pitted in areas other than what needs to be removed to patch the old hole, chuck them.
Carl
