A quick first point. Umar only uses nape hair on the first two lines of hairline grafts. So, I doubt Abedoggs appearance has anything to do with nape hair.
As for gels, my favorite is Matrix hair thickening gel. When I get out of the shower I put a nickel size amount and run it through my frontal 1/3 of my hair. Then I just let my hair dry as normal (because I'm lazy and hair dryers are noisy . )
I also use Nioxin thickening conditioner, but the gel is the big difference maker. I tried different thickening mouses, but the gel works best for me. I have light brown thinner type hair and living in Cali, where there is no humidity, left to their own devices, hairs like mine don't give great coverage.
With the conditioner and gel and only washing my hair every other day, I can get thick coverage.
I also want to add, although I know it doesn't apply to everyone, that getting highlights can also thicken your head of hair. Highlight chemicals damage the hair (not the follicle if done professionally and correctly) which adds to its appearance of thickness.
I get subtle blond highlights (the same color my hair turns if I spend a lot of time in the sun) and this adds to my hairs thickness as well.