I seems to me that you would be giving away the advantage and the profit of buying at a discount:
Where's the advantage to you?
Do you think that you will be buying at 40 cents on the dollar and the Investor would be so altruistic that they would help you out for another 10%?
If you have, say 50% of the money, why don't you just look for an REO, put the 50% down for a very favorable Interest Rate, and have a nice home.
The other pitfalls may make this decision easy for you;
With Trustee Sales, you often do not get to do Inspections and you may not get to do a Title Search.
Think about these things.
Trying to squeeze a little extra discount out of the deal, may cost you a lot.
Good luck and may God bless