Here's a little loop I do that goes right by there... I drop my son off at the fullerton college pool and I have about an hour and a half free.
http://app.strava.com/activities/38401374.
If you were to cut across the middle on Bastunchury you'd find a nasty little hill to go up. (westbound on Bastunchury starting at Associated Rd)
If you want something explicitly hillier, you can check out this route that a friend of mine does when he drops HIS kid off for dance practice -
http://app.strava.com/activities/20893136
Rose/Tustin are pretty good if you need to get north or south, Chapman is fine E of the 57 but I don't particularly care for it west of the 57 (I use commonwealth) and Harbor is fine south of Imperial. North of Imperial it'll shake your fillings out and there are tons of trucks. Brea Blvd is pretty good the whole way too, depending on where you want to go. I don't know if you'll have time to really get into the hills north of Brea/La Habra though, but there's plenty of good riding up there.