Unless they've changed (unlikely) the "optional" bike rack is a receiver hitch that connects to the left and right main frame members. If you look under the trailer, on the rear frame members, maybe 6-8" forward, you should see 4 holes on each side drilled through the frame. The hitch pieces bolt up to those frame members with a 1 1/4" hitch centered in the span. At least that's how it was on my 210WBS unit and a friend's 244.
On my 210WBS, I modified it so that it rode higher (IMHO, it hung too close to the ground) and the 210WBS has a rear bumper, so, I fabricated a stanchion assembly to allow for some bracing using the rear bumper. The hitch will then take any automotive hitch style bike rack that uses a 1 1/4" hitch.
If you don't want to go the FunFinder "option" route, you could just go to any good welder and let him fabricate the same thing...you need a cross frame piece (1 1/2 to 2" box steel) either flange bolted or welded to each main frame member with a 1 1/4" hitch welded to the cross frame at the mid point.
My 2 cents, your mileage may vary...
2 Cats; J-Lo and Ragamuffin :R
2014 Thor Tuscany 40RX DP
2011 Ram 2500 Longhorn CTD HO
2011 Keystone Cougar 318SAB (now gone)
2008 FunFinder X 210WBS (Sadly gone)