You can't do anything except grief with portal blocks. They aren't meant to be manually placed. You should just create a portal normally.
But since we don't want people to build portals anywhere yet and since Nether adds lag currently we will not open it just yet.
My intention will be to allow on the normal server for people to create portals but to dissalow it in the nether. This way, people won't create a portal in the nether that will appear in someone`s house on the normal server. If people build in the nether, a portal can happen inside their home but there is nothing possible to do regarding that.
ZB, Admin, Software developper
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Like others have stated, the closest blocks that could be added would be like clay, bricks, or pumpkins. I would not want these blocks added though because when boredom strikes, I go looking for such blocks that are not in storage.