How to extend from ElggUser

Hey all,

I'm having a problem creating an extension of ElggUser. For example, suppose I have a class "boy" extending ElggUser. If I log in as "boy", then refresh the page, the "boot, system" event triggers some session loading function that tries to get the entity of the user logged in. However, the platform hasn't loaded the "boy" class I've defined yet so it doesn't load the logged in user in the session correctly.

I feel like I'm missing a step somewhere... Help?