Its not "payware" that makes it shine, its the work that goes into it!

Seriously, the shine is made by using an alpha channel, which is just a gray copy of the image overlayed on top of it, in a format called DXT3.  FS sees this as a reflection map: the darker the gray, the more it shines.  For a nearly mirror finish, I would suggest a color in the low 100s with an alpha channel of (0,0,0).  That will make the model nearly blind anyone who looks at it.

You can also paint each different part of the alpha channel a different shade of gray, so that you have different reflectivities for each part.

To make all of this work you need to find and download DXTBmp.  A freeware program that can take the current FS textures of an aircraft apart so you can edit them, then put them back together when you're done.