Fortunately, the capistrano code is nicely organized, and that made it easy for me to add a "noscm" provider that will work with the "copy" deploy strategy to simply copy the projects directory tree to a remote server rather than trying to check it out from the remote server. You can get the code here: http://rubber.rubyforge.org/svn/trunk/lib/capistrano/noscm.rb and then add the following lines to your deploy script to get it to work:
set :scm, :noscm
set :deploy_via, :copy
set :copy_strategy, :export
This works for my limited use case, YMMV - things like "cap deploy:pending:diff" definately won't work as all I've implemented from the capistrano scm interface is the "export" ability.