@Kyle Sullivan
This sounds extremely similar to my girlfriend and I's situation. We're also about 80% of the way there and intent to finish it up after we finish working on a current rental property. We have contacted about 3 banks about getting a HELOC on an investment property and also on the SFH that we live in and are fixing up. Of the three banks that we contacted, one did a drive by appraisal, the other said they would come in and appraise it, and the other said they would do a drive by appraisal.
In your case, and in our case with our SFH, the drive by appraisal would work well. We live on plywood floors and they appraised it as if it were finished because they only drove by. So if you could get a drive by appraisal and have them come up with a number high enough, you might be able to make that work.
Unfortunately for my rental properties, I want them to come in and see the updates rather than just drive by because the drive bys tend to just give you a "middle of the road" appraisal. My rentals after they've been rehabbed look great and would appraise for much higher than a drive by (based on market comps). During a drive by they have no idea whats inside, does it have central AC, washer and dryer, etc?
All in all, contact a few banks and see what appraisal process they use. Good luck!