Unfortunately right now you can't. You'll need to wait for the the official release or be running both iOS 8 and Yosemite for the syncing to occur--however, none of your documents will update on iCloud.com if you do that.
There is no way around that, as these are test servers and not meant for productive use. Apple is pretty clear about that as soon as you open up an iCloud compatible app, in that big box that pops up saying it's not going to sync outside of iOS 8 and Yosemite.
In addition, documents stored inside the test servers are technically not safe from being destroyed. Apple may reset the servers at any point during the testing and definitely will once the beta period is over.