Look for morph.cfg in your DW20 mod pack, and look for this snippet:
Code:
# Disable the flight ability until a player...
# 0 = Enable early game flight
# 1 = ...has reached the nether
# 2 = ...has killed the Wither
I:disableEarlyGameFlight=1
Setting it to "0" makes you "instafly". You need to restart your FTB launcher instance.