Alpha Blending Mixer with alpha values

Hello everyone.

I am using Alpha Blending Mixer in my Qsys Project on Quartus 15.0.

I got the need of using alpha blend option of the core. In the datasheet of VIP Suite I noticed the following "The IP core does not use alpha values for the background layer (a0); you must tie the alpha0 port off to 0 when you instantiate the IP core in the parameter editor."

What's the correct way to instantiate an Avalon Streaming Sink to a hard value of "0" ?

Thanks in advance