I think this is a really bad idea and I am not entirely sure if its legal. People who need a visa sponsorship are not allowed to work for other employers except

I think this is a really bad idea and I am not entirely sure if its legal. People who need a visa sponsorship are not allowed to work for other employers except their sponsoring employer. So your "trial" week idea, while legal, is indirectly preventing sponsorship candidates from applying to your company. You are also discriminating against disabled people or people who cannot leave their current location for extended periods, due to health related conditions, for example people on dialysis. Are you comfortable precluding such people from applying to your company?