Hi Daniel,
You are not going to like my answer, but I recommend do not do that. I think all CMS features (ie features that plug into the content system including Shared Files) should be self contained and not have any dependency on other cms features, they should only depend on mojoPortal core and its sub systems. You should not depend on the existence of another feature and you cannot be sure the feature won't change and break your code. You can borrow code from Shared Files to implement what you need in your own feature but you should not depend on the Shared Files feature from a custom feature. All features included in mojoPortal and all add on features I ship follow this rule.
Best,
Joe