Robo Rally - Alternative rules for option cards?
This uses the online PDF from http://www.wizards.com/avalonhill/rules/roborally.pdf

You aren't allowed to "sit" anywhere.

First: You have to play cards. If you time-out, the player to the right plays random cards to fill out your non-locked registers. (p. 4) Locked registers WILL be played. 

Second:
All movement Cards used but not locked are discarded, as are unused. (p. 4, 8) New ones will be drawn.

Third:
You only get one draw of an option card per turn, and only if you END the turn (and thus also Register 5's phase) on it. Crossing it during the turn doesn't get you the card. (p. 8)

fourth:
The odds are not good in 3p or more that you'll get the cards needed to return to your start space.

Camping on a repair spot is thus not as easy as it may seem. Especially since you retain only locked cards. If one gets consistently lucky enough to have the ability to return to start spot with cards alone, it's great. If one is using terrain, it's skill, more than luck.

In short, I suspect the problem isn't the option cards, but a misread of the rules.

If there was no misread, one simple solution is to use a 1 per space limit; put a (custom) player token on each upgrade spot, and when you draw an option card, put that token on it. When it's lost, put the token on an upgrade slot where you don't have one.

I've never felt it needed, and the people I've known who did usually were making one of three mistakes: 
1) retaining unused programming cards, thus being able to plan multiple turns ahead
2) retaining used programming cards. This makes it a VERY different game. 
3) allowing repairs and upgrades each register phase, rather than only at the end of the turn. This makes camping on a spot far more worthwhile.