Help Restriction For Retail Scheme Buffer (Acis)

Hi guys, i'm trying to make a restriction on aCis Scheme Buffer, so just VIP players can use it, I already installed the VIP system.

I thiking add the check before html pop-up when players talk to npc.

Example:

If player is not a VIP player, don't open the window and say "Only VIP players can use SchemeBuffer" , but is player is vip just open the normal html window.

I need to add this check inside this?

public void onBypassFeedback(L2PcInstance player, String command) 

Thanks for read and response me :)