You may find Lessa Siegele's trick helpful. She masks off an area on any ruler using scotch tape to create the 'grid lines shape' that the specialty ruler uses:
https://thequiltshow.com/watch/free-...e-bom-designer
Fast forward to 39:20. This episode is free to watch until July 31st.
(She has lots of good tricks in this episode though, worth watching the whole thing IMO)