I have never removed anything but the air cleaner. But then again, I usually do just like with you; I figure it out and let somebody else do it (BG).
There is no space for two hands, so you must either try and get the rubber section on the line and then work against the firm nipple or you can shorten the rubber section such that only a half inch extends past the nipple. Being shorter gives some firmness that can allow one hand to push the line into.
Bosch Master, ASE Master, L1
33 years MB technician