Sorry I'm late to this thread as I've been away photographing.
Here's a solution that works well for me...
1. Set up the Print module as if you making your final print - same size, same margins, etc., etc.
2. Take your right margin and drag it over to provide a 2" or 3" test strip. Yes, you are using the same, larger size paper, but you'll be able to make a series of test strips for this photo (and others).
3. Drag your image inside this long, narrow test strip to show the area you want to see proofed. This is what I find really helpful as I can see a strip from top to bottom.
4. Ensure all your print settings are correct and hit Print.
5. Further test strips can be made on the same sheet be dragging your left margin to the right and your right margin another 2" or 3" further right. Surprisingly, Lightroom "remembers" what part of the photo you printed in the previous strip.