Trigger Object via Quest

Im Working on custom Quests (on an up to date 3.3.5 Trinity Server), and now i planned to build a quest where you have to push a Button to get to the Next level. But how do i make it that only players with the Quest can push the Button and those who dont got the quest cant even select the Button. I Know you had to set the Flag to 4 in Gameobject_Template, but where do i connect the Button ID (eg 900001) to the Quest (eg 900001) ?

Flag 4 means you can not interact with this GO. You would have to change this flag back by a script.

But just another idea:

You can set the gameobject as a questgiver (type 2).
Than you can make the GO as a queststarter.
And than you can set some conditions in quest_template. For very special conditions there is the general table conditions.