Of course I have one of those myself, huh!
It hasn't hampered me all that much, though, gotten used to it, I guess.
I do have a 15 gallon kettle of the same, but prefer using the smaller kettle for 5 gallon or split 2 x 3 gallon batches.
The easiest way I get around that too-full-a-kettle-to-boil-comfortably dilemma is by keeping 1-1.5 gallons of last runnings (2nd batch sparge, gravity low 1.020s) aside and boil/simmer that on the stove, by itself. Then add it to the kettle at some later point, when the surface has receded enough, usually around flame-out. I can therefore sparge a little extra to make up for the extra boil off.
Another way I've gotten around it, is by keeping those 1-1.5 gallons of low gravity, last runnings aside and add them to the kettle at flameout. It should keep the whole batch well above 170F, enough to pasteurize that "late boil" addition. I doubt there's enough DMS precursor (SMM) in those last low gravity runnings to be noticeable, I've never noticed it.
Or just add those 1-1.5 gallons of last, low gravity runnings toward the end of the boil, when the surface has receded enough, say, with 10-15 minutes left and bring back to a boil.
Has anyone come up with alternate methods, aside from buying a bigger kettle?