Hi there,if your client wants to use a device which needs non-free firmware then you will need to use another distribution. Trisquel or more specific the Linux libre kernel does not support loading firmware.
It really makes no sense to use Trisquel and install a non-free kernel in order to use non-free firmware.
You should speak with your client and ask if a free supported WLAN stick is acceptable.
HTH,Holger
