That would be rather like doing learning surgery over the
internet. Can't really be done.
I learned casting from reading books 20 years ago and have never had
a workshop in jewelry casting. Taught myself pewter casting also
from reading. The difference in learning casting versus surgery is
that casting mistakes are not fatal, usually anyway. I make a
fulltime living at this and perhaps I am unusual, but it is possible.
The real problems in learning casting comes when one has mastered the
procedure of sprueing, investing, casting, etc. and then the
problems of porosity, incomplete fills, and other ailments start to
surface. These problems require a certain amount of "engineering" to
overcome and will plague even experienced casters at times.
I'm sure that hands on lessons would be the best way to learn, but it
is not impossible to learn from books alone. I believe there are some
videos available also that might really help.