I played around with this and used an env_blood entity, or several, triggered by a normal trigger_multiple (in your case trigger_once would be better). It threw blood onto the glass, but not directly in front of the player. So the glass looked great everywhere else. I had it set to Blood Stream, so I wonder if that makes a difference? All I do know is that increasing the amount of blood above the default 100 doesn't seem to produce more.
Maybe the Decal flag needs to be unchecked? Let me know if you find out.
Andy