Note: I didn't realize this was an old thread when responding, but the info might be useful...
There is a pivot maneuver to get the back wheels across the trench using the backhoe to lift them and the stabilizers to steady everything up (I started another thread on this see
http://www.tractorbynet.com/forums/kubota-owning-operating/167751-bx24-backhoe-pivot-move-over.html).
Check here for a description of the maneuver:
Tips
This works for a full-sized machine (I've seen it done) but the
BX24 seems a little too short to accomplish this. Doing this also takes a bit of nerve since there's a good chance of tipping if you hit the BH swing a bit too hard.
I've used 4x8 sheet stock to cover up one part of the trench to permit digging straight in. That works pretty well except last week when I did this with 12mm aspenite (flakeboard). It was interesting to say the least getting off the trench. Some 3/4 inch plywood works much better.
I line up three or four 4x8s with 8 foot sides across the trench and leap-frog them as I dig and move. That is pretty secure as long as you keep the trench edges free of mounds of dirt that will cause the 4x8 to rest unevenly. The 4x8 will bend a bit but generally won't crack (except for the aspenite :shocked

as long as your wheels aren't on the board directly over the trench. When you are in digging position the 4x8s and wheels are actually supported by the trench edges and the 4x8's effect is mainly to prevent your wheels from falling into the trench and to keep the trench walls from potentially caving in.
The only risky points to this method is moving on and off the trench and boards - thats when your back wheels and the weight of the backhoe would be supported only by the sheet stock. I generally double-up the 4x8 that will take the weight of the back wheels when moving on or off.
The pivot maneuver would be a whole lot simpler but for now I'm sticking with the boards.