Mine (free) http://www.modelfunction.com/ plugin can do this task.

This code works for me:

model = Sketchup.active_model
materials=model.materials

Adds a material as an in model material

m = materials.add "Test Color"
begin

Returns nil if not successful, path if successful

path=Sketchup.find_support_file "1.jpg","\Plugins\"
# m.texture = "1.jpg"
m.texture = path
m.texture.size = 666
rescue
UI.messagebox $!.message
end

I have done it with my new ModelFunction 2.0 that plan to be released very soon. The new version keeps the design in a component quite similare to the SU dynamic component and includes some other improves.
Attached file and video capture
[flash=540,360:tqny54kg]http://www.youtube.com/v/oi_NNOGIZVk[/flash:tqny54kg].

chairs.skp

1.2 is available now via http://modelfunction.com
Major improvements are:

• New language 'lang.xml' file enables changes menus and commands text and language.
• When the designer saves the template, a jpg thumbnail created by plugin and saved in the same directory where the template file is saved.
• New "aiming" function that assists the designer to change axis of a component to axis of 'node'.

Thanks for your interest, the ModelFunction plugin is just published and there is still lot of work to do.
Beta 1.1 is now available here http://www.modelfunction.com/ and offers some improvements and working examples.