I had a situation earlier where I was trying to help someone with an issue. If I upvote all their questions so we can move it to chat, is that ok? They did not have enough rep to chat.
You could always invite the low-rep user to join you for a chat on JabbR.
Note that there is no official affiliation between StackOverflow and JabbR.
As others have said, that's not ok. Votes are supposed to reflect the quality of the thing you're voting on, not artificially bypass thresholds for privileges.
However, that doesn't solve your problem: you want to have a discussion, and (rightly IMO) do not want to have a long discussion in comments. That's not what comments are for either, and by doing it you not only do something bad but set a bad example. Some sites already have too many users who think extended discussions in comments are ok (forum mentality); let's not make it worse.
So how to proceed? This isn't ideal, but you can ask a moderator on your site to add someone to the permission list for the site's chat room. Of course the mod will have to agree and you may need to wait, but very little on SE is so urgent that you need to have that conversation right now, so that's probably ok. I've seen this used occasionally to good effect, and if a particular user turns out to be a problem, this action is easily reversed.
A somewhat long forgotten fact is that there is a completely unofficial IRC channel on Freenode,
#stackoverflow. While we can't guarantee the safety, sanity or purity of any soul daring to venture there, it's usually a rather cozy and friendly place. Nice web based clients exist, you can always invite a user there. Note, questions should still be asked on the main site, but people do get a bit of help there for one off things.
As for voting, you probably would not get into trouble if the posts were of decent quality to begin with. However, if a moderator happens upon an incomprehensible question and notices that it was up-voted, they're going to take a closer look.
Instead, if you feel a post is worth more than one vote, share it on Twitter / etc. If it really is of decent quality and interesting, it's going to get a few more votes rather quickly.