What they said is correct.. If you have another large loader you can lift the excavator boom up with someone releasing the pressure in the cylinder with the levers key on. Once you get the boom in a suitable position, you can free wheel the final drives with the center gear removed. Your gonna need something good sized to get it up a trailer unless field is at same site as house..... 8Ton machine
Be careful, free wheel means free wheel, and they will roll very easy on any slope. I would try to fix in field if at all possible. That is a good size machine I wouldn't want to move around without another machine of comparable size. (small dozer, another excavator.)
Dealer mentioned a pony motor to release hydraulic brake, and power the excavator. This is the best safest idea. You could rig a remote with some long hoses to do the same... Would take some special fittings/tee's might be worth it.