Can threads be used to achieve a subtle non-surgical lip lift?

You are so correct, fillers will only make a long lip worse.  We have effectively used a suture loop to shorten the vertical height of the upper lip.  It's a short procedure under local anesthesia, but you may need to wear a mask for a week to conceal potential bruising.

Hello. Thank you for the question. Threads in the vermilion border can help define the upper lip. Have you ever tried a lip flip with a neuotoxin such as Botox/Dysport/Xeomin? This helps pull the upper lip up to give it more show. It uses a small amount of the neurotoxin and shows results in 2 weeks. 

Hello, 
Thank you for your question. 
I believe you can use a combination. Of Mono and Twist threads to achieve some volumization of the vermilion border of the upper lip especially in the cupid's bow and the philtrum  to achieve the appearance of a shortening of this area. (The results of this can take months to show, there is usually an initial change although the long term effects if the these threads is what would make the most difference).
The use of dermal fillers in the correct areas where there is likely loss of volume and directly on the philtrum as well as your upper and lower lip (to maintain symmetry) would be the way I would approach it. 
I can also understand that if the filler is not done to a very high standard and with the doctor knowing exactly what you want to achieve, it would likely deliver a unsatisfactory result. 
I hope this helps and you find someone who can do this treatment for you. 
Kind Regards
Dr. Joseph Novoa Libermann M.D
A&E and Aesthetic Doctor