We had a similar situation at our club years ago, and for a season (or a series... I forget) what we did was back calculate a bunch of results to the same corrected time and assigned the resultant average rating to everyone.
It worked alright, but for some reason everything reverted soon after.....
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)