How to use Henna hair dye to streak hair?

I want to use henna to streak my hair i have dark brown hair and I brought Mahogany henna cream. My Question is how do I protect my surrounding hair from the henna that I'm using on the section that I'm streaking? I don't want it to "bleed" onto the other sections. Since it's only a couple of streaks, I don't think that a cap is necessary. My first thought was to use a small amount of Vaseline (or something other oil) surrounding the hair I want to streak