|Your solution will most likley get you fired. I say that because you said, "Cause the IT dept refuse to provide a router."|
If you worked where I did, you would be fired instantly and walked off the site. All accounts and access cards would be disabled and any/all keys you had would be taken from you as would your parking pass. All before the security guys had you at your car. You would then be forced to make some arrangements with HR to get any personal items you may have in your office.
We have a policy here where I work that clearly states this type of activity is against the rules and attempting to bypass said policy/rule will get you terminiated "with prejudice" as I said above. From the sounds of it, your place of business has the same policy in place.
What you're talking about doing could down some, or all of the network at your place of work. This is why there's an IT person (or people) who handle things like the network. Because people like you don't know anything about it.
Keep in mind, this is your work. You don't own the computer or the network there and are obliged to abide by the owners of said equipment/network's rules as to how it can be used. You want to surf the web on multiple wireless devices, do it at home.
If they wanted you to waste your time playing angry birds while watching movies on your iPad at work, they'd provide you with a wireless solution.
But you do what you want because I can promise you that they not only watch for people like you (we do, and we always catch them) but, I know there's some hungry go-getter out there ready to take over your job who will abide by the rules and be darn happy to have a job.
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.