Are there legal restrictions on borrowing/lending money to fund employer-provided stock/financial benefits?

My company offers an Employee Stock Purchase Plan, as many public companies do. It is funded by payroll deductions only, and provides an approximate 15% discount on purchase of company stock. If I am unable to afford the maximum allowed deductions, but want to take advantage of the program, are there any restrictions or legal issues with me borrowing money from a family member to offset the deductions? For example, I want to contribute $500 per pay check, my brother would give me the $500 every payday, after 6 periods I would have contributed $3k, receive the discount, sell the shares, and we would split the gains in someway. Both pay required taxes. We see it as a personal loan with specific use-of-funds requirement.