What awg size are the al wires? As Joed said you likely need 4 wires not 3. However 3 wire feeders are allowed if you do not have any other conductive paths going out to that shop like metal water lines or other cables for tv etc .... and your jurisdiction is on a code cycle prior to 2008 and there are no local or state code amendments disallowing 3 wire feeders.
Jeez how did he miss the building by 3 feet? What he should of done was put in a stub up so you could sweep up on the inside wall after the walls went up and come in the bottom of the panel.
If the concrete is poured you don't have much choice but to use the LB you have pictured. At the bottom of the trench install a pvc sweep then a riser length of pvc to the sweep and terminate into the LB. Take the cover off the Lb and pull the wires out of the LB to the length needed to make the proper terminations to the inside panel be sure to measure for the farthest point and then allow allow another 3 feet if possible. Take the wires and bend them over and the pass them back into the LB and out the inside panel. Pull the wires until they are neatly seated into the LB. This will take a little grunt work. Put the cover back on.
I had to chuckle a bit when you implied the electrician didn't want to mess with frozen ground. I think I would pass on him and either finish the wiring yourself or get another electrician that will finish the job you hired him to do.....
How about putting up a picture of the inside panel with the front cover removed...
As Pete said you need to run a #6 bare copper out to a ground rod and protect it where it needs to be when it is exposed. Again not sure why you have to do this if an electrician has been hired....