Lease option or LO Assignment?

[Eric Y.]

I looked at a home that I found fairly nice but after some discussion with the homeowners I'm not sure there's a deal here.  I'm seeing @Brian Gibbons post about lease options but I feel like I may run in to some problems with that.

Here's the deal:

Asking: $89,900

Value: $85,000

Left on Mortgage: $85k 

Market Rent: $1100-$1200/mo

My guess on their PITI: $670

So, they are stuck in this house and motivated (as they have already moved out).  This is a retired couple and I'd like to help but I need to make a profit.

Some notes: Somehow right at the top of the bubble they refi'd to around $110k which is why they are so upside-down.  That may imply that there is more value in the property but I did comps as best I could from recent Zillow sales and I'd rather be conservative.

I have seen @Brian Gibbons talk about lease options and lease option assignments and I mostly understand how the numbers work there.  It's intriguing but I believe you run the risk of the original bank calling the loan.  It is Chase bank so I suspect that they would call it (ie: big corp = not very flexible + rising interest rates providing incentive.)

I do not have the resources to refi the loan if it is called.  The people I'm buying from don't have the resources either.  

So, should I just walk away or is there a safe way to do this?  Maybe go talk to the local Chase branch manager? 

Maybe a "master lease" without option?  I'm not sure there's enough juice to squeeze for that.

Maybe a "master lease option" with a mix of repair options: ie: if it's an expense above $1000 they have to pay for it otherwise I would?