On the side of posted Stack Exchange website questions, there is a side bar that tells you the same site questions that are linked in the post (if any), and below it, there is a "Related" questions box that must do some sort of indexing of the page and finds similar questions. I am proposing a simple "more questions similar to this" link at the bottom of the "Related" tab section.
It could show a popup box similar to the interface of flagging a question/answer. This would also be similar to the "duplicate" tab inside of the flagging UI. It could show the question title, the votes, and an excerpt of the question
It would take you to the site search engine, similar to clicking on the tag score of a user. I prefer this method, because it would add a new feature to the search engine. The callout would look something like
issimilar:[question#]. The search engine would take consider the question title, and the question text. It could also consider the tags, but that shouldn't be a huge part of the search. You would also still be able to use
[tag] in the search. So for this question, it would look like this