Command to post like someone else?

[I5ok4]

I'm trying to use the chat for a pbc rpg and i need a command that allow Admin & Mod to post chat message like someone else for example a npc...

Is there a way to do that without have to use /nick all the time?

hypothetically something like

write:
/npc John=hi dear warrior blablabla 

To output:
Jonh: hi dear warrior blablabla


Sorry for my terrible English ^^"