Demi-permanent color and dark roots

Hi  I'm new around here, and thought I'd try to get some ideas from you nice people.

I've been bleaching my naturally medium-dark brown hair for about 6 months now. I finally grew tired of it and decided to go red. I applied a color filler and Wella Color Charm demi-permanent color in Fiery Red. It turned out quite nice and though it's toned down some since then, I still like it. Now for my question. I know that demi colors don't lift, so I was wondering what would be the best way to lift my dark roots enough to apply the color.

Thanks in advance