Scheduler: drag event to new resource, but keep times

I have a scheduler broken into 15 minute intervals.

Let's say there's an event from 11:05 - 11:35. I want to be able to drag the event to a new resource without changing the times, but only if it's dragged to the same time block.

So, if a 11:05 event on Resource A is dragged to the 11:00 block of Resource B, it should still be 11:05, but if it's changed to the 12:00 block on Resource B, it can change times.

I am aware of SnapToGrid property, but it doesn't perform as desired (it's too easy to change by a minute, for example)