There is a 1.4x teleconverter, the EC14. Read about it atI hadn't heard about an E1 teleconverter or didn't notice it.
http://www.olympusamerica.com/e1/index.html
Go to menu item "The System", pop-up sub-menu item "Accessories", and on the next page select "Lens Accessories". Or browse the whole gee-whiz site!
The official ESP (Estimated Street Price) is US$429 according to
http://www.dpreview.com/news/0308/03082600olyuse1pricing.asp
For my infrequent long focal length needs, that plus the 50-200 would reach 280 true mm, comparable to anything from 310mm to 560mm depending on which comparison you prefer, at f/4.8.