At this time, no. We'd like to get things like this in place. Do you have the resources to try this sort of thing on your own? We could also work with you on this effort if that's of interest to you. Does twiki have any sort of services layer or easy way to export their content?
We are in the process of designing a migration / import framework which would help with this process.
On a similar note, it will also be useful to import data from MediaWiki to Clearspace. We have a lot of info in our MediaWiki installation and I'm importing this to Clearspace manually as I learn how Clearspace works...
MediaWiki has some sort of preliminary API (http://meta.wikimedia.org/wiki/API) that might be useful to transfer data to Clearspace.