First, pull the right wire and leave it somewhere on the block. Then tilt the camera so that you can see the entire plane you want to connect the port to. After that, connect the port to the desired position with indents.

Indention for a Standard Block:

• 3 voxels from the edge of the block.
• 7 voxels between the two ports.
• At the top and bottom, 1 voxel each.

Adding ports at proper indents results in the all too familiar click sound while placing the proper block directly next to it's input or output.