I cant connect to the nintendo WFC because of security.

No. The DS is hardware limited to WEP and no security and the dsi/3ds, assuming they are hacked, don't really offer anything more other than those few games that support DSi extras if that is where you will go next (theoretically with a monster hack on a per game basis you would be able to do more but nobody is going to do that).

Solution is buy an old router you can drop down low enough and set that up as a secondary network, see if you can have a guest network on your main router, make a network on your phone, or make an access point with suitably low security* on a PC with a spare wifi card (this might include the ancient Nintendo adapter but certainly don't go looking for one, and even if you have one it is still likely to be faff compared to the other options for no great gain).

*just because it is WEP and no security does not mean you can't do mac address filtering and other more active approaches, as well as turning it off after you are done.

I usually find the old router approach the easier option, not least of all because I have a stack of old routers when I upgrade them. They also tend to litter places where second hand tat lives, though that might be easier said than done.
If you have a phone though then plenty go for that, and if you have a random old USB wifi card/adapter then that is plenty viable for most too.

 

You could also try a hotspot