Running Eberron Using S&W White Box

I've been pondering running an Eberron game using Swords & Wizardry White Box and I've run into a fairly big snag: racial class restrictions.

No real meaning behind this pic other than that
I really, really like this art work. Pic from WotC.

The White Box has rules for the various non-human races about what classes they can take and the levels that can be attained in those classes. The problem is, Eberron was written and published using D&D 3.5, which didn't have rules like that. It's completely normal in Eberron to have things like half-orc druids, dwarven wizards, halfling clerics, and any other odd-ball race/class combination. It's also expected that those kinds of characters should be gaining experience at the same rate as the rest of the party so that the characters can continue adventuring together without there being a big permanent power disparity.

So for this Eberron game, I'm going to be completely abolishing class and race restrictions. That's easy, but here's the problem: the only real bonus for humans in S&W is an absence of class and race restrictions. Humans can take any class and advance to any level, but that's all they get. So, the problem I'm facing is finding a way to keep humans viable characters. After all, why play a human fighter if you can play a dwarven fighter and get bonus stuff that the human characters don't get?

At first I thought dragonmarks could be a way to buff humans, but other races also get dragonmarks, albeit with less variety. But, it's a good start. Humans may be slightly more likely to manifest a dragonmark than the other races.

Here's my solution: humans get 10% bonus experience on top of bonus experience from high ability scores and an additional 10% chance to manifest a dragonmark. The XP bonus will give the humans a bit of a buff, but it won't be nearly as bad as limiting other races (like the halflings' limitation of 4th level as a fighter). It may not be perfect, but hopefully it'll be a reason to interest my players in humans.