I'm happy to report the issue turned out to be a non-issue.

The hospital wrapped the end of the line in gauze and then put a gauze sleeve over that as protection against airborne germs or accidental snags. When we checked in with AC, we asked for an escort through security and the contact info for the GSC on duty - our escort turned out to be perfect and he knew exactly what to do.

Both parents were in wheelchairs (my poor mother is exhausted from my father's hospital week) and when we noticed the MMW booth was not being used, we switched from Plan A (escort: "I'll tell the screener your father cannot get out of the wheelchair and not to touch his arm and they'll do a quick patdown") to Plan B (go through the WTMD).

Between the 'front of the line' service and the escort handling everything (he even put my father's shoes back on while he sat in the chair) perfectly, it was a complete breeze.

A HUGE kudos and thanks to the Air Canada skycap/escort at PBI!