The fact that an experienced mechanic with what one presumes are better-than-average mechanical skills trashed two Ultegra shift lever bodies would hint to me at poor design/poor execution on Shimano's part.

In industrial fittings where one uses swaged fittings (swaging is the technical name for fittings like the olive that are smushed onto the hose*) like Parker or SwageLok, you can actually buy hardened steel fittings to pre-swage the the "olives*"" to the tube. Then assembly is easy. This might be a nice tool for Shimano to produce.

*Swaging is also how they make double and triple-butted tubes.
** Swagelok doesn't use tubes, it uses two rings that nest. Parker uses a single ring. But the principle's the same: you smush something metal onto the tube and this allows a better seal.