Connect laptops wirelessly to my Tomato router, then have that router pass them to another router...?

Lemme try and explain: our office uses a shared wireless internet connection that the whole building has the SSID and PW for. I want to take this Netgear WNR3500lv2 that I installed tomato-Netgear-3500Lv2-K26USB-1.28.RT-N5x--117-AIO on and do this:

FACT #1: I don't know what kind of router is broadcasting the internet connection for our building and I don't have access to it. I just have the SSID and PW. It's WPA personal AES.

I want to have the laptops in my office and our copier connect to  my Tomato router with my SSID and PW (so no one else in the building can access my copier or my laptops) then have my Tomato router bridge my authenticated laptops and copier to the building's shared SSID for internet access. This way, my laptops and copier will be on the same subnet with eachother so they can share and print, and they'll be able to hit the public internet as well, but I won't be exposed. See what I'm going for here?

The problem is: I can't figure out how to do it with Tomato. I have got it to where if I plug the laptops and copier physically into the ethernet ports on the back of my Tomato router, then the Tomato router successfully connects them to the building's shared SSID and therefore to the internet. I did this by going to "Basic>Network>Wireless Mode>Wireless Ethernet Bridge" and inputting the building's SSID and PW there.

What I can't figure out is - how do I get my Tomato router to broadcast it's own SSID with a PW and subnet determined by me, THEN hand off authenticated clients to the building's internet? How do I "cut the cord"? I can't have the peripherals in the office hardwired to the back of the router due to placement issues. Also, the way I have it set up, it doesn't solve the security issue because the laptops and copier are getting their IP addresses from the building's default gateway, so they are still on the same subnet as every other schmuck in the building and who knows what weirdos in the parking lot?@?!?@?!

Can I do this with the firmware I've installed on my Netgear router? If not, is there a firmware that WILL support this kind of functionality?

Thanks for your help!

pentatonic145