If you're willing to go with the nodded approach, the Secret Rooms Mod should help you out. It adds a variety of hidden blocks such as pressure plates, levers, one-way glass and walk-through blocks.

The mod can be found on the Minecraft Forum.

If you feel like using the modded approach, the Secret Rooms Mod should help you out. It adds a variety of hidden blocks such as pressure plates, levers, one-way glass and walk-through blocks.

The mod can be found on the Minecraft Forum.

If you're willing to go with the nodded approach, the Secret Rooms Mod should help you out. It adds a variety of hidden blocks such as pressure plates, levers, one-way glass and walk-through blocks.

The mod can be found on the Minecraft Forum.

As far as I know, it's not exactly possible to have an invisible pressure plate in Vanilla Minecraft.

If you're willing to go with the nodded approach, the Secret Rooms Mod should help you out. It adds a variety of hidden blocks such as pressure plates, levers, one-way glass and walk-through blocks.

The mod can be found on the Minecraft Forum.