Use Graphics.CopyFromScreen To Enable Alpha Transparent Controls?

I am trying to use (and this may be my problem already) e.Graphics.CopyFromScreen() in the OnPaint() method of my control to prepare a background onto which I can draw the content of the control. The goal is a tool-tip with rounded corners and other specific features to replace the default Windows tool tip.

Ideally the tool tip could be antialiased and blended into the backdrop, however at a pinch I could tolerate an aliased boundary. This may also be necessary as the control will often be covering a control with an OpenGL overlay and the whole blending procedure may end up a nightmare.

I have created a custom user control, a persistent instance of which belonds to my applications's main form, overriding the OnPaint and OnPaintBackground methods. The application of transparency however is challenging. As I understand, the graphics object passed to the paint method starts with a copy of the current VisibleClipBounds, where generally the first move is to clear the control with a solid colour and start drawing the main features. My first thought was to bypass the fill and start drawing on the captured background. For the first redraw this works fine, but subsequent redraws keep the previous content instead of re-capturing the backdrop. I hoped that CopyFromScreen would specifically eliminate the currently drawing control from its capture so as to start from a clean base but this is not the case, it captures the rectangle of the new location including the image of the previous location if it is in the bounds.