Trading out folding bike seat post
Yes

Of course it's possible, you just need to find a telescopic seat post on the market that is longer than the one you have. 

Your measurement of your post might be a bit off though, I'm guessing that from your 28.x measurement, and the fact that I don't think 34.2mm is a seatpost size... not one that I'm familiar with anyways. In which case chances are your post is a 34.9mm, not a 34.2mm, and that something like this will do the trick:

34.9mm EXTRA LONG EXTENDABLE SEAT POST 530mm-730mm(21"-28") TELESCOPIC ALLOY