There are some special commands for redrawing DCs that are not in the main API docs, but the DC docs and other sources...
This has a ...
dcs = $dc_observers.get_latest_class dcs.redraw_with_undo(sang)
example
http://stackoverflow.com/questions/8507476/sketchup-dynamic-component-options-manipulating-from-ruby
Or here https://groups.google.com/forum/?fromgroups=#!topic/sketchupruby/630uerkDhJI
There are also several posts at SCF, like this one http://sketchucation.com/forums/viewtopic.php?f=180&t=41567