Beard Growth, bald strips

I have always had two spots in my beard that refuse to grow any hair at all. They are slightly diagonal strips that separate the edges of my goatee and the beard hair of my cheek on both sides. They are not large, by any means, but do cause a noticeable division between the goatee and the cheek hair. I was wondering if there is any way to stimulate growth there? The skin is smooth and seems very healthy, just hairless, and it has always been that way.

I was thinking about something along the lines of applying rogaine or something similar to these spots but I've looked around and found that even if it worked, I would probably have to constantly apply it for continuous growth there. I've even read in places that Lavender Oil might help, but I want to be sure. Anyone have any ideas?