I think the ATAN2 function will do what you want. Just change the I,J offsets.
The easier way if you want to make the entire pocket larger than the mail part, plug in a slightly smaller tool size than the actual tool size into the CAM program and the pocket will come out oversize. For instance, if you have a 1 inch diameter pocket and you are using a 0.250 cutter, then tell the CAM program that the tool is 0.245 and the pocket should come out 1.010 dia. If the CAM program has something like a stock to leave (might be labeled roughing clearance, or something like that), then try plugging in a negative value of the amount of oversize you want.