Actually, I played in a game where a Weaponmaster used his bow a lot - mostly because his player was afraid of tanking. He didn't like getting hit, and really didn't like taking damage.
His mark is still effective at range, but he couldn't do anything to enforce it, so it played more like a half-assed controller.
As a build though, you would need something else to make it work. Mark of Warding would help (mark penalty is -3), and you would likely want to poach multiattack powers so you can mark many things at once. So you'd want to be a half elf, and multiclass into Ranger (probably), but at the end of the day, you're still only half a character, as you have no way to punish your enemies for violating your mark.
Alternately you might want to grab the new monk multiclass that gives you Unarmed Strike so that you can punish adjacent enemies while still wielding a bow in your other hand.
Regardless, there are better ways to do it.
I like your Slayer houserule (and thought up a similar one last year for bow slayers when the book first came out). Haven't tried it yet though.