You can do it. Boiled water is rid of oxygen, for all intents and purposes. Just transfer the water "quietly" so as to not introduce more oxygen.
Also know that it will dilute ABV, IBUs, and Gravity. You can calculate each of these with the following formula:
C1V1 = C2V2
C = Concentration (ABV, IBUs or Gravity- use whole numbers only)
V = Volume (in your case, V1 = 4, v2 = 5)
and just solve for C2