How do I get my dog to play when she loses interest but still clearly has energy?

My 8mo border collie mix seems to lose interest in games very quickly, especially if only me or my wife is out there (can't play alone, need everyone together). She'll chase a ball, or frisbee, or run around with us for a few minutes only, and then just lays down and won't engage. She clearly still has energy and wants to play, because after we bring her inside she'll be romping around with her toys. I'd like to find things that can keep her engaged for more than a minute or two for running, but so far everything is hit and miss.

I'm thinking of getting one of those egg shaped balls or something that she can herd and roll around, but beyond that I'm stumped with how to tire this dog out.