What about this twist:
The psion is not able to remainfest the power on himself while the current power is active, but what if he readies an action to remanifest once the power ends. So for his turn he readies the power, his turn ends, he remanifests the power, continuous coverage.
Would this work? Also, you could say that his opponent could ready an action to attack once he recasts, but how could he tell when it is being recast since it's a purely mental action. There is some type of display associated but this can be easily suppressed with a successful concentration check.