Using object model it will be quite simple. Suppose you have list of changesets you want to display. Then you may have use VersionControlServer method GetChangeset to retrieve Changeset object by id, and that object will have WorkItems collection with associated work items.
The issue here may be how to identify latest changesets. Here I would go for some simple (if not altogether elegant) solution - to get latest changeset ID created it is possible to use GetLatestChangesetId method of VersionControlServer, and then you may simply use all changesets IDs between latest id and (latest id - N).
Generally, about VSTS extensibility you might want to have a look at Buck Hodges blog (and more specifically at simple Version Control example).
Hope that helps.