Searching the forum archives, uncovers more discussion on this topic.
In it, disturbing though in particular are the contrary views at Reply 3 (USA expert) and Reply 4 (UK expert).
Goto: re: Don't roll or bu mp start y our syncro in revers e
Should ask Rudi I suppose but meanwhile from my past experience, if the need arises, I roll down my street till reaching about 15-20 kmh, then ignition on, engage 3RD gear and then EASE OUT the clutch. No strain discernible.
Years ago I experienced far from help, both flat starting AND camping battery plus an inability to clutch start due to no slope to roll down. Solution for me that got the engine running was to combine the residual energy of the two (flat) batteries utilising previously installed upgraded cables and switchible connector. Lesson learnt.