IMO, 1st step is getting the lengths of each side of the triangular mounting area. 2nd step would be comparing how they are mounted. I’ve never taken mine off, but I’m guessing it’s a few screws or something. If the screw placement is different among mirrors/doors, then you would have to drill new holes in whatever mirror you were using and match it up with the door. Again though, not sure how the mirrors mount to the door.
I would have to see “cut” mirrors up close to really judge, I’m a bit skeptical of how clean that would look.
And here’s another idea, maybe not doable. But what if it were possible to just swap the upper and lower portions of mirrors? 98 Accord owners would have to get at least '99 mirrors in this case (since '99 was the first year for folding mirrors), but I am wondering if the lower portion (that’s attached to the door) of say, a 1999 side mirror housing, would accept the upper portion (that's the folding part) of a mirror from 99-03 TL’s/CL’s. This may be too out there...
Btw, swollen_cu has an 01 TL, someone could ask him to measure his triangular mounting area.