Using cable ties is fine but of course it does mean the cage isn’t rigid as the grids can move and bend on the cable ties - they act like hinges effectively. This may or may not be a problem depending on how and where you are setting it up.
Could you ask somebody to pop the connectors on for you - family, friend, neighbour?
I use c&c grids as my spare cage when my boys come indoors and it is cable tied together so I can concertina it up for storage