Yes I have the Renogy Portable Suitcase,the 20 ft cable that I bought is very flexible.
You can get that cable and hook the MC4 connector to the pigtail from the controller to the extension then put the flat pole on it so it would mate up to your existing setup. Which should work out just fine.
I have seen reports of others that have done the same with no problems.
The reason I did not do this is that the pig tail from the controller is 14 AWG and the extension is 12AWG. I wanted the same Gauge wire all the way from controller to the battery,at that length I wanted less loss of voltage. I used the MC4 connectors for a better connection and better waterproof protection.