The one reason why i really wanted to get that pixel what is behind.
Tried all those blending flags what are in the page you gave.
You have to disable the depth buffer for this:
and afterwards reenable
Never use the zbuffer with alpha-blended stuff, it just doesn't work.
You can actually leave on GL_DEPTH_TEST and just set glDepthMask to false, otherwise your alphablended stuff will probably overlap your opaque geometry. Also, if you have a texture that is eigther fully opague and on some pixels fully transparent, you can just leave z-buffering like normal and just use alpha-testing by adding this line to your shader after the texture read:
if(tex.a <= 0.0001f) discard;