This is my take on a base clamp for Fanatec.

My desk has a quite a bit of depth, therefore, when using the wheel with the normal base clamp the wheel is hanging out too much off the table (see photos for comparison).

With this design (100mm offset used in the photos) the wheel sits about perfect for my use case with the formula v2.5x wheel. 

The design is based on the Bessey TK6 clamps ( https://www.amazon.es/dp/B000JLSNAE?psc=1&ref=ppx_yo2ov_dt_b_product_details ), but any clamp with up to 9mm diameter and no more than 100mm depth will fit just right.

This design uses M6x15mm tapered screws with the factory attachments for the base. I believe that M6x20mm will also work.

I strongly recommend applying some anti-slip material to the bottom of the clamp to ensure that it will not move around when playing.

The wheel is tilted 12 degrees. If you want a special version, just let me know in the comments and I will configure the tilt and offset for you!

This model was inspired by the following: https://www.thingiverse.com/thing:4973948