Glue is going to give you the most undetectable front hairline. Depending on the density and the style of cut, tape can do fine, but...depending on the type of tape there can be a hint of shine as well as more of a ridge. I think if you had walker no shine or a dulled tape in the front you would be alright with putting tape behind the glue. Problems might be that the ridge might make it harder for the glue to adhere to the lace since the lace won't be 100% flat after the tape. Also the possibility that the tape breaks down before the glue could become and issue. I would try it for a week and see how it works. I am sure this is something that plenty of wearers actually do and i bet works fine once perfected and with the right combination of products.

I have about 63% in the front and use walker no-shine tape. I use tape mainly because I like the ease of use and clean up. Glue is more time consuming and I find that tape looks really good at the hairline, but everyone is different. Its what every works for you honestly.