Wig wearers with larger heads...some advice?

[pyro-fae.livejournal.com]

I tried to wear a wig for the first time this weekend; I tried wearing it twice throughout the weekend. Both times ended up with me taking it off before the end of the day due to major head pain. The problem seems to be that the wig cap is simply too tight on my extremely large head (it's a family trait). I've tried putting the wig cap over something to stretch it out but it still seems to be overly tight. Do any other large-headed wig wearers have tips on how to wear their wigs comfortably?

Note: The wig is a larger-sized one, and it definitely fits my head. It just seems the wig cap is the trouble.