Hello John,
the solution is really simple.
just use the -rml and -rmf switches to specify the librariy(ies) and the name of the rootmapfile.
For example, starting from the line you use in the previous post:
rootcling -f dictToto.cxx -rml libtoto.so -rmf libtoto.rootmap myHeader1.h myHeader2.h ... LinkDef.h
For more help: rootcling -v.
Cheers,
Danilo