I found this interesting because the armrests I have offered up as a prize in the short story competition are exactly the same.
I decided there was no way I could make it fit on the left, hence the offer!
I wondered about the domed piece but didn't want to cut my handles. In fact it isn't necessary, the bracket can go flush against the seat, and the handles stick out a bit, looks funny though.
There isn't actually a domed bit on the seat, the stuffing stops short around the hole, so the end of the cone goes down to the metal/rubber bushing and the seat material fluffs up around the dome to look good.
Seems to me the cut off dome is a good idea, but I don't know about blodging the bracket
I did consider making a piece of something to go over the bracket dome outside of the mounting plate so it would look better than just the straight bracket, but the only way I could see to fix the heat control thing was to cut a hole in the bracket, then it would rust etc.
I just told the missus she couldn't have armrests.