a pump that is the correct length (and that has peg fittings) won't fall out of the pump pegs but it may not survive being on the bike when it is parked either.
I'd suggest that (if you can't find a pump with a dual head the right length, which is quite likely) you buy a pump that does the most common type of valve and use an adaptor for the other sort.
BTW a lot of Dutch bikes have pump pegs on the rack and a dealer in the same may well be able to provide a suitable pump.
cheers