Actually, gankers do quite often get their own lanes, although ranged carries are the most important. Ranged Carries -> Gankers -> Melee Carries is the usual list of "who gets the lane". It really depends on a hero; any specific heroes you seeing getting a solo lane that you think shouldn't?
Not really sure how to force a lane switch. Might want to google it. I know they will switch if you just walk into their lane, and I know there is a way to make them switch in DotA 1.
My advice is to try not to get stuck in a lane like that (Sniper might be food for a ganking Butcher, but in-lane, butcher has no chance). If you cant help it, get a Stout Shield; it is decent on just about any melee hero except for Leviathan (who comes with his built-in.). Sniper's damage is reduced to almost nothing early-game by a Stout Shield, although his attacks do go through it 40% of the time.
But yea, don't solo a lane with a hero your not 100% confident in using. And dont put two melees (or three, if you are doing a tri-lane) into the same lane, that is just asking for trouble. Its not as easy with AI allies, but when you have been outlaned by a human, pull a ganker off another lane to kill him with you. Pudge is, however, an amazing solo ganker. Turn on Rot, Hook someone right after, then Dismember them when they are pulled next to you. Instantly kills most people early game and will take out squishy support heroes... forever.