i too, like BmoreDrew & Scrodzilla, am confused why you seem to be so hung-up on slamming your wheel all the way forward in the dropouts?

what makes you think that you can't tighten the nuts down enuff to keep it from sliding without tugs? plus then you have to change the chain length every time you switch cog size. maybe a half-link chain really is the best thing for you after all.

as far as replacing your cog...
all you need is an ordinary 9-spline cog, they are all over the place for as little as $3-4. do you really need a homebrewed on your deadeye? those are meant for the stress of serious mtbing. since you likely will need to buy several cogs anyway to try different gear ratios now that you've learned that mountain bike gearing is not so great for riding pavement, why not keep your cost down till you find the gear ratio you like best?

good luck...