Refinancing A Seller Finance Deal

[John Laliberte]

Hi everyone, thanks in advance for any advice on this one.

I am trying to figure out the best way to finance a 4-plex.  

Here is the issue: 

The owner we are working with is approaching retirement and we estimate he would enjoy some passive income without the hassle of landlording.  We believe we can get a favorable deal done through a longer term seller finance of maybe 15-20 years. 

The property needs an extremely healthy amount of CapEx. The capital for renovations will come directly from myself and my partner.

Say we renovate and the property will appraise at a considerably higher value, how do regain our capital and maintain the seller finance terms?

If we cash-out refi with a bank, the seller loses his terms, correct?  Is there a way to pull out the equity we force on the property and maintain the seller finance terms?

Thanks for any input!