Crop an image to a shape, both already in the document

[herosz]

Hy!
I created a nice shape by edit his points, now I want to apply to a picture that already is in my document.

1. If I proceed: Shape → fill shape → picture → I can insert picture only from my hard disk or Network place, , not my existent picture from the document.
2. If I proceed: Picture → Crop to shape → I can insert only predefined shapes, not my existent shape from the document.

So is any method to use an existent shape with an existent picture? (both are already in the document, I don't want to reedit the shape or export the picture in a file).