Trying: a network gate that has a MAC filter and WiFi passthru

Ls,

New to this forum. Nice to meet you.

I don't know if what I am trying is possible, and perhaps far easier with an additional router, but I just threw that away so... I'm trying the following:

I have a pc with a wifi dongle and am using my neighbours Wifi router(with his permission!=)
There is another, vintage, computer wich has a PCMCIA wifi card thats... very old. It only uses WEP encryption.
My neighbours router uses WPA2, also old (or according to my iPhone) but usable.
Long story short: they ain't talking to each other.
I tried adding the MAC address of the PCMCIA card to the routers pass-thru filter; which should have worked! If I hadn't read the checkboxes wrong and ended up only allowing my MAC address. This led him to be locked out and he didn't like that at all.
So he still allows me on his router but no more adding MAC addresses.

Anyhoe... so I thought up another plan, this might require another router to work but perhaps it can be done without.
I hope someone can assist me if it is possible.

Since my PC has access to the internet through the wifi dongle;
Can I set up some kind of software gateway that will also use the dongle to connect to the PCMCIA wifi card based on the MAC address and piggy back that connection to his router over the WPA2 encrypted connection on my neighbours wifi router?

Sounds very illegal/hacky (for some reason) but trust me, my neighbour knows me(he's my neighbour) and is fine with it.
The computer i'm trying to connect is an old Amiga1200.
I read somewhere I might be able to flash the PCMCIA card to be able to use WPA2 as well but its very hard to find the firmware.
Also, apparently, WPA is much to heavy for the Amiga.
So my idea for just using WEP + MAC address access and using the PC for the WPA2 seems viable.
Then again, me brain don't think so good or I wouldn't be asking.

Thank you for reading this far

Regards,
Mac