I’m going to disagree with @Chris Seveney and say whether an assignee could force a sale directly would be a state law issue and heavily dependent upon the contract terms. 

What are the terms of the lease?

I am wanting to get into fix and flips and eventually long term rentals. 

This forces prices down long term.

You set your own payment terms with YOUR client and then find funding for them.The Capital Syndicate is a private lender firm that offers financing through their own company, but they also provide you with a list of about 150 other private lenders. 

Hard money loans can be an option, but they often come with high-interest rates and short repayment terms.

You can force appreciation by rehabbing and such - so that might be a shorter term way to go?  

Has anybody found a workaround for this or would the seller simply have to hold the note long-term without the option of selling it?

As for Cash flow, I think it depends on the deal structure as you mentioned, but also strategy/approach (cash flow vs building asset, holding long term).

A lot of rehab lenders will account previous reno expereince when it comes to terms.