Convert WEP to WPA/2 (WEP device on WPA2 network) (virtual router?)

Hey so, I'm asking to see if i can get any help on this.

I have a WPA2 wireless setup on my router, but I'm trying to get my Nintendo DS Lite (which only supports WEP) to talk to my 3DS.

I really don't WANT to convert my entire network to WEP just for one device, as I know that's a bad idea.

I have a D-Link DIR-657, it's a great router for what I "need," but what I'd like to do is like have a guest network setup on WEP, but I can only run the guest network on the same security as my real one.

Is this something that maybe custom firmware could solve? If so can you link me a guide on how to go about setting up multiple networks with different security settings works.
 
You can use DD-WRT, create a separate VLAN and attach the second network to that and use a different encryption. I did not check if your router was compatible.

One other option is to use a second router and use a mac address filter of only your DS. That way even when they compromise WEP they will only be able to see your IP packets from DS to router, they wont be able to use your wifi or compromise any other machine on network.
 
And the annoying thing is I SORT OF got it to "work" the way I was hoping, but it just rejects it still:

Sg2cJTB.png