You can use a bitmap to create a brush and you can convert an extrusion to a bitmap filled shape. Create your extrusion and convert to editable shapes you will now have a shape with a bit map fill. you can use this or any bitmap to create a brush in the same way you would create a brush with a vector object or group once you have created your brush click the edit brush button on the info bar and on the fill properties tab clear the check mark from the tile fills box and you can edit your brush just as you normally would. One thing though you can not use named colours on a bitmap brush to make it colour changeable.