That's different. Wireless feature is hard coded in each DS ROM. To add WPA and WPA2 support would require all DS cartridges recall.Its a stupid Limitation Nintendo decided to not fix. Sony fixed the PS Vita PSP Mode WiFi Problem the Right way allowing PSP games to use the Vita's Wireless N card via some sort of wrapper so that PSP games have Internet access on a WPA2 only Wireless N only network even.
Nintendo could of easily did this also, instead,we got WEP for Flashcards and WPA1 for DSi games. only 3DS games and apps can use WPA2.
Your options are,
* Get the discontinued Nintendo USB WiFi adapter. The connection is proprietary.
* Get a router that supports multiple SSID.
* Get a Mini USB adapter and plug into your PC. Set up a WEP access point and use it when you need to.