Using Uri with Google Maps API

Hello 
 

 I’m trying to use Uri to create a Google Maps request (https://developers.google.com/maps/documentation/distancematrix/) and i find it a bit awkward since the API uses pipe character for separating parameter values but Uri uses commas and i could not find a way to override it:
 

 utop # open Core.Std;;
 utop # #require "uri";;
 utop # let x = Uri.of_string "http://www.github.com/";;
 val x : Uri.t = <abstr>          
 utop # let y = Uri.add_query_param x ("origins", ["Bristol"; "Cambridge"; "Plymouth"; "London"]);;
 val y : Uri.t = <abstr>       
 utop # Uri.to_string y;;
 - : string = "http://www.github.com/?origins=Bristol,Cambridge,Plymouth,London" 
 

 I tried doing this but as you can see it performed character escape on pipe characters (so besides looking ugly it did not work):
 

 utop # String.concat ~sep:"|" ["Bristol"; "Cambridge"; "Plymouth"; "London"];;
 - : string = "Bristol|Cambridge|Plymouth|London"   
 utop # let y = Uri.add_query_param x ("origins", [c]);;
 val y : Uri.t = <abstr> 
 utop # Uri.to_string y;;
 - : string = "http://www.github.com/?origins=Bristol%7CCambridge%7CPlymouth%7CLondon"
 

 Help?!
 

 -- Ollie