We love our corner bed, but I agree it's not as easy to make as a walk around bed. Here's how I minimize the fitted sheet fun:
1. Put mattress cover and flannel fitted sheet on mattress. We only do this once per season.
2. Use the flat flannel sheet as the new bottom sheet by just tucking it down around the edges and under the corner that is accessible. I'm sure this would work with regular cotton sheets as well, but I bought flannel and figured they may "stick" together better between the fitted and the fake-fitted (flat sheet).
3. Use a spare flat sheet as your actual flat sheet (we had one on hand from a set where the fitted sheet got destroyed). Lay it on the bed and tuck it in at the bottom edge (and/or sides, if you prefer).
4. Now put your comforter on as usual.
5. When you come back from a trip, just take the two flat sheets off to wash them. Once per season (or at some frequency that suits you), take the fitted sheet and mattress cover off to wash. Now you only have to put those on occasionally, rather than at every washing!