They make one small enough, I wouldn't try to make one. Three are way too many connections to make and the prefabbed ones really are that much better. Making a big harness may be plausible but a small one no way! I just looked it up and realized that they come sized as small as for a green cheek conure but not lovebird:
http://www.theparrotuniversity.com/aviator_harness.phpSorry. I guess harness flying isn't really available for such a small bird. The problem is that the connections can only get so small. Even the X-Small harness looks disproportionately oversized on Kili. It looks like an adult seatbelt on a small child. When you look at a large parrot in a harness, you can see a length of strap between connections. On Kili, the harness tightens down practically to the point where the connections are practically together with barely any strap between them. Seeing the design of this harness and others, it seems quite unlikely you can make one yourself. I do know one person that makes a special harness for budgies but they are a specialty item so I'm not sure how effective it would be for parrot flight.