Switching users of same group in linux

My environment is like:

   I have two users 'user1' and 'user2' both are in same group(say group name is 'abc') in server 'server1'. Now I have another server 'server2' which have user 'user2'. user2 in both the servers are exchanged their public keys (I mean to say authentication configured properly).

Now requirement is like :

  I have to perform a copy operation on server2 (both source and destination folders are in server2 only) from server1 as user2(because identity file configuration done successfully as said above), but currently I have loggedin as user1, user1 doesn't have permissions to use 'su' to switch to user2 (not only user1 all users belongs 'abc' group are don't have permission to use 'su').

question is like :

1. How can i perform copy operation on server2 without using su (or anyothe command like su, my expectation is from boot files)...?

Thanks in advance, Sivea.