Sites such as these do exist and are usually called "coin mixing" services. Not sure which ones are trust worthy because the first ones I noticed were on Tor. You could check the trade page
https://en.bitcoin.it/wiki/Trade and look under the financial services section to see what mixing sites are available.
Yes, there a couple, I don't like the login idea though. I understand that he wants you to be able to split the coins to make it harder to trace but by using two addresses and having a long deadline for the "overflow" address you can achieve much the same thing.
It doesn't seem like to popular of an idea though. (surprised me) I'll wait for a few more opinions before I decide to do it or not.