+1 But, consider the following...
My request is similar, though in my situation, I need a raft only under the bed contact portion of the part, and not necessarily the supports, and the raft needs to take into account INSIDE part perimeter, not just the outside perimeter. Since we are talking time and excess, it is of equal importance I feel to address this.
I continuously print hold-down plates for various heat-sinks...well the use is not important anyways. But the plates more or less are the equivalent to a picture frame in shape. It's also a shape which likes to bow if not stuck firmly to the bed. The raft feature however, you could say, is printing the entire "picture" inside of the "frame", when all I need is to raft support the frame itself with raft exterior overhang calculated on the interior perimeter as the exterior perimeter. It definitely is eating much excess filament and time which has made me hesitant to even use rafts when making these. Thus, I'm cutting corners by creating attached skirts not to use the heavily excess rafting. Skirts give me outside sanding work in this scenario, but a raft will pull off and not effect the exterior look of said hold-down plates since bottom cosmetic is not important. That is my justification for desiring this feature. Please consider both circumstances at play.