osia: hide first bar line on left hand of key signature

[Konstatin Heuer]

Is it possible to hide the first bar line 
on the left hand of the key signature when writing ossia?

Or:

Is it possible to get the same result like with 

\remove "System_start_delimiter_engraver"

between some Staffs only?


So as to synchronize several GrandStaffs, that are not meant to be one score. 


Thank you very much for your reply