In the faq:
I need to submit multiple values as...
By default, if more than one value appears in the post request for the same field/key, they will be joined by the 'separator' value like &post-values=a,b,c.
However, if you use [] as the separator it will instead create multiple keys like &post-values[]=a&post-values[]=b&....
Use [#] to retain the numerical index: &post-values[0]=a&post-values[1]=b&...
Although now that I think of it I might not have exposed a setting to customize the delimiter. Please check and let me know if it's working for you.