I've done this a number of times, similar to Mike's suggestion....altho' I've done it on meganite...which is similar to corian. I use a fluted round over bit. my questions to you would be, are they true blood grooves, and do they run off to the sink, i.e., drain board style ? I've always built jigs..picture a wooden box with edge guides and rails that the router "glides" on, with a slight taper (on the rails the router glides on) so that there is drainage to the sink. If it's not into the sink, the end tapers are more radical, running up to meet the counter in a nice "flow" at both ends. regardless, I run the bit just short of it's straight vertical shoulder cut, so the roundover blends nicely right into the countertop....so you are running the bit like 1/16th shy of where it's curve meets it sharp vertical. The bit is the same used to make fluted columns. Hope this helps.