We have created a mapping of Wikidata Qids to Freebase Mids, and are publishing it under CC0, so that anyone can use it in any way they want. The file contains about 2 Million mappings.
Since the data is published under CC0, it can be uploaded to Wikidata. We also plan to upload the data to Freebase. The two-way links would ensure that systems using either knowledge base can easily merge data, go from one to the other, enrich data with each other, etc. We opted to first publish the mappings standalone, to make clear that they are under CC0.
The mapping is created based on the Wikidata dumps from end of October. Wikidata Items are matched with Freebase Topics based on their respective links to Wikipedia. Each mapping says that there have been no disagreeing Wikipedia-Links and at least two agreeing Wikipedia-Links, so the data should be very clean. Furthermore, the mappings are sorted by the number of agreeing Wikipedia-Links, so it is kinda sorted by relevance.
The data is in RDF format. To get the Mids as they are used in Wikidata, the replace the namespace http://rdf.freebase.com/ns/m
The Wikidata Qids are using the Wikidata namespace, i.e. the Qids themselves are concatenated to http://www.wikidata.org/entity/
If anyone wants to take up the task to upload the data to Wikidata, I can offer to help and answer questions.