Why duct tape over plain sports tape or hockey tape? I know hockey tape is almost the same as sports tape, just less flexible, and it's cheap stuff. Duct tape I find quite irritating on the skin, it's not meant for skin.
This one lady during a random offhand conversation about figure skating, she said back in the days of the floppy boots, they'd put foam padding around the ankles, so it's possible if you can find a thick grade of padding and sorta wrap it around her ankles or shove it in the gaps? Probably a combo of foam pads/tape.
http://www.grafskates.com/411.0.html?&L=1 That's Graf's contact info for Graf Switzerland and Germany. Also gives Graf Canada, but Graf Canada's website (as far as I can tell) doesn't list anything for figure skating. So it could be a problem either on Graf Canada's end, or a problem on Graf Switzerland's end. But those are numbers you can call directly if need be.