Could you make the population of the user's attributes lazy? If so, you could keep track of all the ones that haven't yet been populated, and the first time an accessor is used from one of the many newly created user objects, the whole list of those that haven't yet been loaded could be prepared and loaded at once, within your class. This would fix the issue of the database being hit with a bunch of little queries, and would require only a small amount of additional bookkeeping within the class, to track which objects hadn't yet been populated so that they can all be populated together in hopefully a quicker transaction, when an accessor is used. If you're concerned with a big lag hitting from time to time, you could set a limit to how many unpopulated objects may exist, and when the limit is reached, run your query again.
Update: Bah! There seems to be an echo in here. Sorry for parroting previously-provided advice.