it's up to the staff they'll let you check in or not

if asking friendly (without overcrowded counters):
it will be possible (we did it often all over the world)

if you go to the biz/first counter with an eco tkt
showing your silver card like a pp of diplomatic corps:
they can send you back to the eco line (good feeling!)

so it's up to you - but no "written privilege" - have fun!