There's not a simple way to do this in Cut2D, but there are at least 2 workarounds.
1) If you did your drawing in another program, offset the profile vectors by whatever amount you want the finish pass to be, then use one vector for roughing, and one for finishing.
2) Create a "roughing" tool in your tooltable with a fake diameter. Say you're using a .25" tool, and want to leave .01" for a finishing pass. Just Tell Cut2D that the tool is .27" diameter, and it will leave .01" for the finishing pass.
V-Carve Pro allows you to to do both methods much easier, having both an offset tool, and an allowance setting on the profile toolpaths to leave material for a finishing pass.
Cut2D is intended as an entry level package, at a much lower price, so doesn't include these tools or options.