I know this is a bit of a late reply, but I know two ways to Minimise sticky notes in Windows 8 and I *think* that one of these methods works with Windows 7.
In Windows 8 (and I think in Windows 7), using the "Show Desktop" keyboard shortcut: Win + D clears the Desktop and the sticky notes are available in the Task Bar.
In Windows 8, Sticky Notes can also be Minimised by using the new, enhanced Task Manager. By expanding the Task Manager item for Sticky Notes and then right-clicking on the lower Sticky Notes item, there is an option to Minimise:
Perhaps, some bright spark like Brink can use this to create a small app that can toggle the Sticky Notes by toggling a registry setting
I hope this helps.