Group ride with a bunch of your racing buddies. Have them go hard enough to make you two work HARD, but not so hard as to totally drop you (my stoker's advice). Kayla HATES being on the slowest bike and will put in really hard efforts to ride with the fast singles. If we are riding hard around here the topography usually does a good job of providing interval work.. We just need to have a "rabbit" to chase so that we don't ride slow when the road starts going up.