Hey, MMWyrm -
The Vikings (and other seafaring peoples) were known to row hundreds of miles upstream to raid targets well inland. Of course, that requires a vessel equipped with oars, and probably a crew larger than two.
Hmm... so two guys (would they need more?) could pole a 30-foot loaded boat up a river? That might work.
Possibly, if the water is shallow enough. I'm not sure how deep it's realistic to pole, but I would think a wooden pole more than about fifteen feet long would have to be pretty thick to move a boat that size without breaking. And if the bottom is muddy or silty, there's a good chance of losing the pole, or just of not going anywhere....
A bit crazy, but I was thinking of them somehow pulling themselves up the river with ropes attached to something on shore (this is a fantasy story - no magic though), but that would just run the boat aground I guess.
Not sure it would necessarily run the boat aground, especially if you had poles and/or a rudder to keep it away from the side. It sounds awfully inefficient, though. You would have to tie the ropes off, get back on the boat, pull, get out, move the ropes upriver and tie them off again, get back in the boat, pull, etc. Much more efficient (assuming you have two guys to move the boat, as you suggested) for one guy to get out and walk along the bank with a rope tied around his waist while the other keeps the boat off the bank. When the one gets tired, they can trade places.
Of course, if your guys are amateurs at all this, you could have them try one method, figure out it doesn't work, try another, figure out it's inefficient, then finally figure out how to do it. Then, if you come up with a better idea, they can run into an old guy who says "Why the hell are you doing it that way?" and explains an even easier method.
Hope this helps.
HN