Sure:
This is not the texture I will be using, I just found this one via google image-search. I currently use placeholders while figuring out how I am going to approach this. The white box represents the actual bounds of the red healthbar-texture.
The first one is just the full healthbar. The second one is how it would currently look, the texture would just be scaled down on the x-axis. In this specific example it’s not horrible since there is not alot of details where you would notice a lot of the scaling, but it’s definitly visible. The third bar is how I would like it to be. I would like to essentially make a part of the texture invisible.
Now I’m really interested about those UV-tricks you are talking about 
In my case it’s not a huge deal: I could either live with the scaling and just create a texture where it’s not extremely distracting, or I could draw another texture above the healthbar which just has the color of the background. Unfortunately this would mean, that the background would have to just be one color or else it would propably look really weird.
If there is a way to do it though and it’s not well above my skilllevel, that would be ideal. I’m pretty sure knowing some way of doing this would also be useful to know when designing new UI-things later.