entertaining thread...think i need another cup!
being one that enjoys a nice cup when trolling thru the morning schlog when coupin. i have considering the bike bottle mount also. In the interim, everyone of us being a vintage/classic motoring enthusiast 'already' has the coffee holder in the emergency road side repair kit: that very handy roll of duct tape!
if its a new roll it will have a girth to it for stability, the center hole diameter fits just about every beverage form, coffee or soda, on its side the roll has just enough tack to it to keep it in place when put on the floor, kinda like Velco/hook & loop feel. just place the roll on the floor on its side and put your cup in the center whole.
when not in use, it the cup holder disappears by just sliding it under the seat...always on the ready for...??
the ten millionth use of a roll of duct tape has worked for me quite well. the cup will need a lid to keep from spilling while corning before the 'holder' will slip....trust me.

-shanon