Doesn't help your aching thumbs much...but, this tight fitting thing is down to the manufacturer's tolerances on the rims and tyres.
Schwalbe's technical manual
"Fitting difficulties often arise when the diameters of the rim and the tire do not match perfectly.
Rims can have a diameter tolerance of ± 0.5 mm. In addition, each rim flange height can also have a tolerance of
± 0.5 mm. These figures add up to a total diameter tolerance of ± 1.5 mm, or 4.7 mm over the circumference. This corresponds to a maximum possible circumferential difference of 9.4 mm between the largest and the smallest rim.
A tire has to fit on both extremes, so because a safe fit has to be ensured even on the smallest permissible rim diameter, the proper fitting of the tire on the largest permissible rim can prove quite difficult.
The circumferential tolerance of SCHWALBE tires is ± 1 mm."
Rest those thumbs!,
All the best,
Pause, take a breath and ask yourself: "What would Rastamouse