It would be very handy to find duplicates in your code. Maybe it is easy to say that you only have to search for real text which is duplicate, so no lexing, parsing, language independent, etc. This is my thinking, but I might be wrong.
If you want to make a threshold to find 100% or 90% or 80% duplicated code, then there must be an other solution.
I would prefer an action for the project and for the file and live scanning the code with an option to disable it.