That's exactly what I've been using in my mobile for several years. I believe it is a six foot cord with double female coupler that I bought from Radio Shack. I have never had an issue with it.
From: stpatryck <firstname.lastname@example.org>
Sent: Monday, July 8, 2013 1:41 PM
Subject: [IC-7000] mic extension cord
Was wondering if I could use a regular RJ-45 extension cord from Radio Shack or Staples without modifying it.