Documenting for future reference but might be useful for others; Fitting Continental GP5000TL to Mavic Cosmic Pro UST carbon rims. Before discovering this method I took the wheels to the local bike shop and none of them could make it work.
Put the tyre in the oven for no more then 5 minutes on a low temperature (gas mark 1). Put a bit of lubricant around the centre of the rim.
Working quickly while tyre is hot
Put one side of the tyre into the centre channel all the way round, starting opposite from the valve
By hand put the other side into the centre of the rim until you get about 1/3 left
Using levers get the next bit in, working a bit each side by levering them over the edge of the rim, favouring one side.
At about 1/4 you'll have about 2" of tyre to still get over the centre and it will be super tight. It looks impossible.
At all times hold the tyre lever in on the side closest to the valve core, do not let this release
Now use the tyre bead seating tool to lift the lip of the tyre one inch away from the tyre lever and while the strongest friend you have pushes the tyre lever towards the valve core with all their strength.
Once on air leaked around the valve stopping inflation so just needed to press the tyre down by hand above the valve.
It is possible to fit in less then 5 minutes this way. Unless your name is Ganesha, you are not fitting this tyre solo. You are not fitting this tyre without a bead seating tool. I don't think I'll be a repeat customer and expect I'll be replacing once half worn to reduce puncture risk.
Now need to get a sealant injector as it will be impossible to fill it up while putting this wheel in with the amount of work needed to do the last bit. Got some air leaking out by the bead/rim edge on the front wheel which I expect will seal OK afterwards.
I've got a similar worry - GP5000 non TL on Roval carbon rims - insanely difficult to get on in the warmth of the house, god help me if I ever needed to fix a puncture out on the road in the cold/rain. They are the sole reason I now carry three tyre levers and two tubes as I'm banking on the certainty I will pinch a tube and snap a lever. At 50% they're coming off and going onto my kids bikes.