Tax relief please!

Mr A and Mrs B are married

Mr A is an employee of a company not related to Mrs B, he is not a director.

Mrs B is a sole trader with losses as at 05.04.11 of £15k+

Mr A wishes to spent £25,000 on a new unit for Mrs B's business

Mr A would obviously like to get some return on the cost of the loan he is taking out to fund the purchase.

An "at arms length" rental agreement may well be challenged by HMRC and would not be beneficial from a tax point of view, as income would be being moved from non-tax paying Mrs B to tax paying Mr A.

Mr A could become a partner with an agreement that profits would be allocated after the loan interest costs were allocated to Mr A. But this would only seem to work if the partnership continues to make losses! 

Mr A and Mrs B are not keen on the idea of Mr A forming a limited company to receive the rent, and taking the income via divdends.

Has anyone got any ideas?