HP stream 11; Broadcom BCM 43142; install to USB

[Ron Leach]

List, good afternoon,

How might I manage to install XFCE onto a laptop equipped only with 
WiFi, but unable to establish a connection because the wireless card 
requires a recent non-free firmware component for the Broadcom BCM 43142?

I'd like to try, and then probably install, the current XFCE release 
onto an HP Stream 11 Notebook PC.

This machine has a potentially useful spec but is limited to:

32GB MMC SDD HD,
2 x USB,
WiFi BCM 43142

http://h20195.www2.hp.com/v2/default.aspx?cc=ie&lc=en&oid=8245635

There is no wired Ethernet LAN connector.  I'd like to run XFCE live 
on this, first, and then would prefer to install XFCE onto a USB 
stick, so that I can leave the (rather small) MMC SDD HD running 
Windows - I need to drop back to Windows for Excel (and Word), 
sometimes (mainly in instances where Libre Office isn't sufficiently 
compatible).

I am not sure how or where I should both:

(a) obtain the required driver, and
(b) once obtained, how to persuade either
   (i) the Live XFCE spin to install the driver (if available), or
   (ii) Ensure that any subsequent install onto USB is able to install 
the Broadcom driver

I could download the driver using another machine which does have 
connectivity, and copy the driver onto an SD card which could be read 
by XFCE on the HP Stream notebook.  But I do not know how to install 
the driver into Fedora, either when running live, nor when fully 
installed.

I'd be grateful for any ideas,

regards, Ron