I have done a bit of reading around on this subject (there is not much at the moment!). The short answer seems to be no.
The long answer is yes, if you reaaally want to. The main difference between the hubs for the standard alfine 11 (sg-s700) and di2 alfine 11 (sg-s705) is in a few parts on the hub that mesh with the cassette joint/motor unit.
SG-S700 uses a multi-tooth gear shaped plate to mesh with the cassette joint. If you look at the hub without the cassette joint fitted then you should see this plate positioned just above where the sprocket sits. SG-S705 uses a different round plate with two grooves on opposite sides of the plate. The plate also has two red dots that have to be lined up with the normal red dots on the hub using a special tool (TL-SGE1).
There also appears to be a difference in the right-hand cone, right-hand lock nut and right hand lock nut washers. I think these are different because of the different shapes of the meshing plates.
So the long answer is that you need to get your hands on these additional parts, pull the SG-S700 hub apart, and swap them over. Otherwise the di2 motor unit will not lock onto the hub. At least I think this is the case - I have not found a seller of the the di2 spare parts yet. When I do, I plan to have a go at modifying my alfine 11.
If you want to know where I got this information from, then here are two documents I found floating around on the internet: