Well, there's the simple option:
Well, there's the simple option:
Stay out of Italy entirely and force the Germans to back up the Italians on both big islands and up and down the western and southern/southeastern coasts.
Basically, turn the entire peninsula into the same sort of defensive sink Norway was; a salient, vulnerable to sea and air power that the Axis could only defend with infantry, artillery, and concrete.
Use the various SOE, OSS, SBS, SAS, etc to keep things hopping, along with various deception operations, and the 12th, 15th, and MAF, plus the Mediterranean Fleet when necessary just to stir things up... nothing ruins your day like a 15 inch shell.
Depending on when this decision is made, either OVERLORD (or ROUNDUP) can be executed early, and ANVIL/DRAGOON follows, or at the very least, if the historical timeframes follow, the available German mobile forces and air power will be even more dispersed then they were historically.
Best,