You really don't need to change the recipe at all. It will turn out identical with no changes made.
IF you want to get picky about it:
Difference in hop utilization for the FWH from 2 hours to 1 hour boil goes from about 25% to about 23%, a factor of 25/23 = 1.09, which means if you wanted absolute identical results, you could add an extra 0.04 ounce of the FWH if you wish to get the same IBUs. Otherwise you might see a reduction of 2 IBUs. 0.04 ounce is like 1 gram, if your scale can even measure that small (mine has trouble measuring this). Meanwhile, human beings are unable to distinguish differences in IBUs less than about 3-4 IBUs. So to a human being, 21 IBUs tastes exactly the same as 23 IBUs anyway. So this whole discussion is truly a moot point. So...
You really don't need to change the recipe at all. It will turn out identical with no changes made.