That is one way. Another is to boil some hops in a DME mix with 1.040 gravity for about an hour, cool and add to your carboy. How much volume you will need for that is beyond me.
A tea of water and hops would work, it just wouldn't be as bitter (someone may need to second this opinion) and would dilute your kolsch.
Long range forecast:
5G Carboy Primary (1):
5G Carboy Primary (2):
2.5G Carboy Primary:
Kegged: alt, Belgo Clone Wars, Salt n' Peppa IPA, Slip One to the Porter, Russian Oligarch Stout, Rye Around Sally IPA, California Commoner, No Fail Cream Ale.