There are lots of tricks to making repairwork more efficient and less-invasive to the instrument. I do a lot of my work through instrument soundholes and cleats to secure cracks are a pretty normal necessary item to keep old instruments healthy. This patient is a 1930s Gibson HG-00 and it's had a rough life filled with many botched repair attempts to numerous hairline cracks. They were never cleated -- only drop-filled -- so I spent the earlier part of the day regluing back braces, cleating the back, and finally cleating the top.
In the above photo you can see that I've marked-out locations on the top where I want cleats on the bottom. I check inside with a mirror and then use my soundhole clamp's bottom foot (the part that's on the inside) to locate places I can put cleats between the braces. When I find good spots, I let the top foot (directly above the bottom) down on the soundboard and mark the spot with a bit of tape.
The only "hard part" of this job is making sure the cleats go on with their grain at a right angle to the top's grain -- as they should be. It's easy enough to bump the cleat around on braces under the top.
Here's another use for the blue painter's tape! I needed to reglue this damaged lute bridge but clamps were not going to do it on that crazy body shape. Since the top was dead flat I didn't need a huge amount of pressure to clamp this one tight to conform it to a distorted soundboard (like on most guitars).
The solution here was to wrap the tape over the bridge and around the body several times (to make it stronger) and then curl the edges into a thick "band" over the bridge. Using shims under the tape I applied enough pressure on the bridge to squeeze out all the excess glue and "clamp" it down tight. Sometimes you just have to think dumber, right?