Well, there is also ForEachEntityDo that iterates over all objects. You can use the same callback (well, maybe change its name to ForEachEntityDoCallback to avoid confusion) and the same calling code except change this line:
ForEachEntityInAABBDo(aabb, reinterpret_cast<byte*>(ForEachEntityInAABBDoCallback), reinterpret_cast<byte*>(entities));
in this line:
ForEachEntityDo(reinterpret_cast<byte*>(ForEachEntityDoCallback), reinterpret_cast<byte*>(entities));
and then simply iterate over entities and do EntityDistance(source, destination).
Cheers!