Hey I think I found something better than X-Mouse for you.
Try editing the shortcut you are using to launch the Steam client, Right Click, Properties, edit TARGET to this:
"C\Program Files (x86)\Steam\steam.exe" -silent
There's a space between the last " and -silent.
Of if your shortcut has a different Target just add -silent to the end of it.
Lemme know if this works for you.