Adding Tamiya clear gloss to paint, anyone use this technique?

I usually just spray my flat Tamiya paints, then give the model a coat of clear gloss before decalling.  I have heard of mixing in some Tamiya clear gloss in with the paint and then spraying it, helping to acheive a more glossy paint without needing a glosscoat for the decals.  Does anyone here do that, and if so- how much clear do you add to your paint?  Also, are there any things to be wary of when doing it this way, such as extended drying times?  TIA!