Depending on what you are trying to do, you have to use different approaches.  

Does anyone have any suggestions on how to approach this situation?

It's normally good practice to manage your rental property finances separate from your personal finances, so that's how I'd approach it.

@Dustin Allen provides a great explanation for how to approach determining the value of that additional piece of land.

If this occurs when using a private lender, what's the best approach for this situation?

Doing both of these simultaneously would be the best approach to getting your first flip done ASAP (in my opinion). 

Sounds like you’ve kinda tried this approach but hoping I provided a little help.

As alluded to in the prior post, both have the same or similar lead generation approach, so potentially having both approaches in place gives you that flexibility. 

By using a data-driven approach to all our property selection, staging, and pricing and occupancy metrics, along with an interview process with the owners, we have developed a great system for aligning with the right owners.

If it were my building I would offer two approaches: cost averaging or in-season surcharge.