A couple things here from reading through the thread...
1. ATC will NOT give you terrain clearance even if they do give you a clearance departing a field. For example: If you file direct, and in the clearance they say "cleared as filed", you dont have to use the ODP (for part 91), but there is NO terrain separation.
2. If you file Direct, and get the clearance "cleared as filed", then you may use the ODP and it will be protected airspace for you (Part 135 and 121 are required to use the ODP when IFR).
3. When there is no ODP, DP, or SID, (and there are many airports that dont have them), the Instrument flying handbook states that you fly runway heading to 400 AGL, or the end of the runway (whatever is last) then proceed to first filed waypoint.
4. ATC will not usually give a clearance in class G airspace. Usually the clearance is something like "upon reaching controlled airspace, cleared to xxx AF etc".
5. Except when necessary for takeoffs and landings, its not legal to fly in class G airspace below minimum flight altitudes (1000 feet, or 2000 feet mountainous). Yes, you dont need a clearance (cant get one) in class G airspace,but you must obey all IFR rules. Chances of meeting these requirements are slim in class G airspace from my experience.
I was once flying VFR with mountains surrounding me. Weather was getting to the point that I needed an IFR, so I asked ATC for a pop-up. Well they couldnt get me one until I was 12000 feet because I was blow the MEA. The problem was that I coudnt get up to that altitude without going in the clouds.
Finally figured out that I could land at an airport that happened to be right under me, I picked up an IFR, did the ODP. After comfortably cruising on top, ATC came on and said "I see what you did there, very clever and sneaky".