I'm not sure about the easing disparities, but it should be pretty trivial to knock out a JSFL script that executes rake from Authoring if you want to expose your build process to the design team.
Another idea that would be kind of painful to maintain - you could create some slightly different build tasks for authoring-driven builds eg;
MXMLC.new(:compile_main) do |t|
t.cp << flex_path
end
MXMLC.new(:compile_main_from_auth) do |t|
t.cp << auth_path
end
To be honest, we usually treat authoring builds as code-free asset libraries whenever possible and then simply point our engineering builds at the resulting asset swf. This generally does limit the amount and type of work that can be done in authoring, but if your application is in any way dynamic, the last thing you want is timeline driven animations anyway.
Luke