I am a cabinet maker and trim carpenter. If you do take a chance with a circular saw for the long straight cuts, drop the saw into the stock, (use EXTREME caution if you must move saw backwards), stop just short of the radius corners, then take drywall screws and drive into all 4 long kerfs (about center to avoid sole of jig saw). This will hold the stock in place as you finish corner radius cuts. Remove screws to let waste drop into plastic suspender below. I do this all the time when cutting out sink holes in plastic countertops.