I don't live in an area where time constraints are *that* extreme, for sure, but I just don't see why you couldn't just finish out the whole TB once you are already at 4-4. Around here, even in timed USTA league matches, if you are within like 5 minutes of finishing a match when time is up, the convention is for the next people with the court (which is generally also going to be a USTA league match) to just let you finish it out. This works out fine because the people who have the court after them will also give them the same courtesy, if needed, unless they are the last match on for the night, in which case the person overseeing the courts is also typically lenient about leaving the lights on a bit past time so people can finish. (note: this is for league matches, where all parties seem to agree that its just better to finish out the matches if possible, the same thing doesn't apply to people in non-league matches, even if they are keeping score).
I guess its possible in other places this type of thing just wouldn't work, but I must say I much prefer it all these other stories about standing around with stopwatches and yelling time in the middle of match point or some other such sillyness.