Yes you can! You put both extenders on the same channel (1-3) so that they share the same adhoc network. Then, you assign different unique extender id for each extenders (0-F) so that the Prontos can address extenders individually.

Note that PEP2.4 support adhoc (standalone) mode just like the PEP1 versions did. The only difference is migration to use MyDatabase which Peter Dewildt put up a sticky post on how to do this years ago.