Hi Rob,
Actually, it is very difficult to install a Rohloff hub on the single-sided rear wheel mounting of Strida
http://en.wikipedia.org/wiki/Strida#Disadvantages
although there are Rohloff hubs for belt drive.
http://www.rohloff.de/en/news/news_rss/news_in_detail/archive/2009/14/september/article/Gates_Carbon_Drive_with_Rohloff_SPEEDHUB_50014-1/index.html
Installing crank gears on Strida is much easier.
[url]Multi-speed modification on Strida]
[url]Has anyone retrofitted a schlumpf on their strida?]
[url]Two alternatives to Schlumpf Speed Drive?]
[url]7 speed STRIDA???]
[url]18 speed gearbox: Good for Strida?]
However, I think it is still possible to install hub gears on Strida. Here is a solution of fitting a rear hub gear to Strida proposed by Mark Sanders 
http://picasaweb.google.com/MAS.DPL/StridaArchivePIX#5301187503381874450
Cheers
Amuro