I'm assuming you use a manual? If you have a local place that makes counter tops for kitchens. Go see them and ask if they will sell you the sink cutouts. I used to do that years ago and made a ton of specialty platens for the manual press. Either run a router, or table saw and groove the platen. Great for butt prints also. If on an auto, left chest, we cut a squeege to about 4 inches, clamped it in and printed. I agree with the rest, thin the ink otherwise it "globbs" on the seam, even with a grooved platen. Just make sure the customer knows what this is going to look like. If to much is "gloobed" on the seam, you may have issues with drying, watch this.
Terry