Good reason not to us 0+00 to start. A station equation would be a good way to go but you would have to be happy with some station back value.
Insert a point on the alignment at the pgl elevation. Pull station 0+00 to the new location and add whatever other edits are required. When you are done project the point to the profile view and autocad move your layout profile to the projected point.
Joseph D. Bouza, P.E. (one of 'THOSE' People) Civil 3D 2012 & 2013 HP Z210 Workstation Intel Xeon CPU E31240 @ 3.30 Hz 12 GB Ram
Note: Its all Resistentialism, so keep calm and carry on