I was redesigning my workshop and I saw a Power Coil break a block when the thought hit me: can Power Coils break Mantle? The answer is yes! I used a regular Workbench Power Coil and a Workbench at altitudes 2 and 3 to successfully break many Mantle blocks. You need to use a set up similar to this:
|EM|EM|WK| Altitude 4
|CO|MA|MA| Altitude 3
EM stands for empty space, CO for Power Coil, WK for closest Workbench block to the coil, and MA is for Mantle. Of course, you also cannot place Workbenches outside of a beacon, so you need to plot the area, but the coil will send a current through the Mantle and to the Workbench and break the Mantle block, just like any game block.
Mantle does not drop anything and there seems to be a universal layer of Mantle at altitude 1, so escaping the world does not seem to be possible. I doubt breaking Mantle is useful for anything beyond flattening the ground at the bottom of the world, but it is interesting to know that it is possible.
EDIT: Somebody beat me to this idea >.> I just did a search and Jiivita already has done a video on this. Ignore me :-p