I ordered a couple of 2.5mm spacers. I'm going to put them between the left crank arm and the BB bearing. If this can work for about an hour I'll be satisfied. I'm not looking to permanently mount the power meter on the CX bike. Rather, I'm just very interested in measuring and recording power during an actual race so as to inform my future training efforts. I'll reply back after I receive and install them on whether it was successful or not.

https://www.ebay.com/itm/301413528334