Hi there,
WE feel your pain, 
You can see some the methods I used to attach/mount to PCB check out those threads.
The Xiao has been around for a good while now, a refresh is coming I’m feeling. The battery issue, and other items would be improved with a New Nordic chip also I would think. It’s not impossible as you can see from those posts of a PC board I’m using.
HTH
GL 
PJ 