It looks like you were successful but I wanted to include a step-by-step guide in the hopes that it is helpful to others.
- Checkout
trunk
into a working copy with depth = “Only this item” - Open working copy
- Go to repo browser from the working copy
- Select your desired project subfolder(s), right-click and select “Update item to revision”
This will pull only the subfolder(s) you’ve selected into your working copy.