OK, Where is the start button
 

How does one ask their SO to at least consider poly?

Hi and welcome! There are a gazillion threads here on this topic. Have you done a search and/or read any of the threads in The Life Stories or Poly Relationships sections?

I have read a few but didn't find any on pre-poly just on starting after an agreement has been made.
thanks for the lead

Have a look at the threads tagged "lessons" and "foundations" to get and idea of what has worked for others and then start talking about what poly means to you. For everyone it's a different but has the same foundation. Its important to know where you want to head with this.