I think personally that it all comes down to communication. If you have been "lapped" by a car early in a qualifier and you tale them for the next few laps, just ask if you can come back through but always accept the fact that they are within their rights to say no. If they're a good enough driver, they'll assess the situation and decide whether it is worthwhile letting you go or not... however, if you are lapped late on in a race, with say a minute to go, it is inappropriate for you to expect to be allowed to unlap yourself as you have no time to rescue your run, and the guy lapping you is on the most crucial laps of his race.
Let's remember that if you have been lapped, you may not be a lap down, if you're on a very short track and you have a 10 second stagger back from the leader, if you crash early they may lap you on lap 3 or 4 maybe earlier... at these times, if you rejoin the track and are right on the leader, just ask for a gap... it may well be beneficial to both.
The key is, communication... always work together with your fellow racers on the rostrum, in qualifying you are all sharing the track to race against the clock... so play nicely...
never impede and don't have full blown conversations or arguments over it as that's not fair on the other 8 guys.
Yardy