Hey, just saw this... I've done something similar, moving a strap button from the bottom of ther bass up to a spot into the belly curve. It's worked with Fender style basses, but I found that on a Thunderbird, just leaving the strap button in it's original spot but arranging the strap over the front of that long lower bout really kinda does the trick.
The top button placed behind the neck also helps. The ergos of the T-bird are very different than the Fender shape, and after some time spent I found myself feeling less awkward and having come to terms with it. Now it's the most comfortable of my three basses.
Anyhow, try the lower strap button in the original place, and put the strap over the front. I got that from
@JIO...