We do not use cups but do use bottle water all the time.. As a quick trip to the store for us is at least 100 miles and often 200 or more Even if we want a an IN & OUT burger its 200 miles.. (California thing) ...

I have found that the water will ride out of the way for the passenger at the corner of the seat near the radio.. Setting on the floor.. and it will stay there thru all the corners and only falls over on hard stops.. Its out of the way and is an area that we do not use.. There is no way it could be put there for the driver as it would end up under foot...
My wife feels that we could make some thing or buy a holder and attach it on the side of the consul where there is carpet beside that part of the seat on both sides.. It would not leave holes that we would notice if we take it off... It would not spill on the switches..as it could be a little lower.... If it were made right it would be out of the way.. and could perhaps be made to hold a cup..

Truth is there is little room in the 124 and the good hanging places are plastic and break easy..

I do like my 123 TDT as it does have more room in the front for passenger comfort.. When my wife and I both travel to different places its always a race to see who gets stuck the the 92 300 CE.. My wife does miss her 123 coupe and lets me know often..

Ken