Hi
A named driver claim will always affect the policyholders premium.
The only way around this is for your flatmate to take out separate temporary insurance cover. If you look at the dayinsure online site, it allows someone to insure a car for which they are not the owner and registered keeper for up to 28 days. If they have a claim it would then be under the temporary insurance and not affect your policy.
Your friend should enquire whether dayinsure are willing to provide cover, when you may also have access to the car and have your own policy for it. I am just thinking they may not be happy when two people could have access to the car at the same time.
The only question is, do you trust your flatmate to pay the Insurance excess on the temp policy, to ensure the car gets repaired. And that they take time off work if necessary to deal with it.
Huckster