Thinking about your issue........OUCH.....note to self, quite thinking, pulls brain muscles.........Harken recomends "typically" anyhow from what I have seen, is a bungy cord that will offer some tension on the aft side of the car to help it pull back if need be. Altho I have seen some setups with lines running aft too, to possibly work in your suggested case.
Anyway, initially when I do the line carrs etc, I am going to skip the rear line/bungie option, and if needed, add it later. Otherwise, I found while crewing on a C&C 115 for the NOODS and the first Ballard monay night series, that at least on that rig, rear lines/bungies were not needed to move the carr back ward.
For the new 155, I found that the approx 4" from one pin hole to the next was good, but really needed a few stops in the middle to get proper leech curve.
So any way, as I said before, hopefully I can get some holes drilled before the comming weekends regatta so we have a bit more options with the new 155 for adjustments.
She drives me boat,
I drives me dinghy!