I must correct my answer/question above: WLC doesn't seem to support EAP-TTLS for local EAP. As @Amjad Abdullah stated, EAP-TTLS will work if you're not involving WLC directly, ie. directly between RADIUS and a WPA supplicant.

I believe that's because WLC simply doesn't support EAP-TTLS. I'm looking for this too instead of EAP-TLS, and it doesn't seem to offer this feature:Should I get a more recent version of WLC software? Mine is 8.2.100.0.