I know exactly what you are discribing. My 2011 Roadster has had that condition since new, now has 24000kms. May have gotten a little worse over time but I accept it now.
The vibration starts at around 2200rpm, fades out around 2500rpm then stays in. With slightest pressure on the clutch lever it disappears completely.
From the feed back on this forum some don't have any vibration and others have it worse than others. But now one has the solution.
I have taken it up with Triumph Australia and mention on every survey Triumph has sent me but no solutions.
Let me know what the dealer comes up with.