IF you aren't living there I believe the answer is no, any contributions would need to be a gift. 

You can get gift funds from a family member to help you qualify - I always recommend using a low down payment option for any owner occupied purchase.

$100 gift cards for $70 at Vancouver wa Costco for Miller paint.

So, recently I was prequalified for (x) amount of dollars through a mortgage broker - it is solely based off of my debt-to-income, but I am using "gifted funds" from my fiancee for part of my downpayment/closing costs.

The home my wife and I live in was gifted to us.

I have a gift of finding wholesale properties apparently.

Ideally the want to give me a Gift of Equity (market value - remainder of existing mortgage) as a down payment.

I could gift the downpayment (which requires some paperwork) and have my sister be the one on the loan.

don't look a gift horse in the mouth... 

I think in return you could provide a welcome gift and thank you for letting you get things ready - this could be something simple like a thank you card and a gift card, welcome mat, or hand soap - something people would need when they are first moving in!