That's certainly a solid point: though it is worth considering how slow a slog even OTL's fight up the penninsula was, which in a scenario where the Germans have eliminated the eastern front is likely to be an even more difficult affair. It's hard to nail down any specifics of exactly how we get to a ceasefire without a timeline of just when Ivan throws in the towel: I'm just trying to construct a framework that meets the OP specifications. It probably would have to be in 42 or very early 43 to not veer into extremely unlikely territory...
I'll say the most likely model is one of a Soviet surrender in late 42 which would allow the Germans to stiffen Italy's spine and give a morale-propaganda shot in the arm to keep Mussolini in power with the Italian military in play to dissuade or defeat an Operation Huskey. That allows for a potentially viable Fortress Europe.
Oh, it certainly took forever, I agree, so it may seem untenable from a political standpoint, especially if you have certain setbacks.
Perhaps even if the US and all didn't cease in attempting Huskey, but managed to succeed (albeit possibly later), you could see toeholds established, but fighting even bloodier and going north (and with more obvious German support). Time is
Perhaps even Churchill gets his Balkan front, and tons of men and material are wasted there trying to liberate Greece and Yugoslavia. So you have a parallel front slowly marching up the boot and the Balkans. Without the Soviets, further diversionary attempts are made to pry off the periphery of German control. Norway is invaded to attempt to liberate that.as well and regain some control of the North Sea and capture German garrisons. And, no matter what, the cost is grisly (though here it takes a lot of bad luck for everything to go terribly).
And, in the end, you have the Allies in control of the Mediterranean islands, the southern bit of italy and maybe even Greece/Albania/Macedonia, Norway, but the politicians don't think it's worth going any farther and that too many lives have been lost. Something like that.
But yeah. Germany can't do anything to help Southeast Asia. The biggest question is what happens to the European colonies sans any European governments reasserting control, but aside from that...