I have a similar problem, but think I can help you Bas-
first check out this link: http://www.flashmagazine.com/Tutorials/detail/away3d_basics_6_-_bitmap_materials/
Another option is to use Prefab3d to create a compatible AS3 class. Prefab3d will let you assign your texture pretty easily. I believe it uses your UV mapping set in your collada file.
My problem is that I want to create an interactive (with mouse events) material in Flash CS5 and apply this to my custom 3d object (I made a mobius strip in Blender). I tried using Prefab 3d but it seems to only allow adding an image file as a texture. Will Away3d allow me to map the material correctly? Is there anyway to adjust UV mapping?
I haven’t been able to embed textures and add them to my Prefab3d created object after importing into Flash builder. I get an unusual pop-up error 1037. This leads me to believe I would have to assign custom textures within the AS3 class generated by Prefab.
FYI- I am a total newb using Away3d v3.6, Flash (aka Flex) Builder 4.5 and Flash 5.0