Idea about Builders...

Hello,
I'm Moran Jung, playing COC in South Korea. :p:p:p
Well, today, while play with my friends and chat via messenger,
notice that friend 'M' needs more builders,
but friend 'W' having 3 extra Builders - cause of he not on upgrading Town Hall 7.
W says, the builder only can use the Wall.

In this situation...
I said(likely joke) 'How about send W's builder to M?';););)
M & W : Oh, that's good! :eek::eek::eek:
W : And get reward 'Dark Elixer'? hahaha-! :cool::cool::cool:
M : That's Fair trade. :o:o:o
- the conversation finish -

Anyway, Can't just give like battle troop's,
but if possible I want to send my builders to help friends or clan members.
- Oh, and to avoid using this action bad... better to give limitation.

Thanks for reading.
And if the idea already known and posted,
ops!:o