Yes jamming it across is the tough part. I guess part of the reason is the base coat is dry and last layer of glue is still fresh. Plus the idea is not slide the thing aound the whole rim, but only a section of it that is enough to allow you to adjust the position.
A piece of steel cable is even easier to use as it has far less surface area.
The only brand of tubulars I know of that's a royal PITA to mount is Continental. Especially on Campa rims.
You can stretch them for a decade, they just don't seem to stretch or if they do they regain their original shape as soon as they're off the rim....
In general the more supple (high true TPI count) the tub the easier it will be to fit. Vitto or Veloflex in particular do not even need to be pre-stretched IME.