To do this, you will need the correct bellows, an Arca-Swiss L bracket and a QR clamp with special foot to adapt the L bracket to the rear function carrier.
That is it.
With the A7 you can go fairly wide, down to 32mm, and increase wide angle look even more, by stitching side-by-sides.
Bellows is 071040 for Sony, L bracket is 802306, and the QR block is 802030.
Hope this helps.