alas. it would appear that UNIVERSAL::isa and UNIVERSAL::can will not be much help in detecting classes which do not appear in use statements

use Receipt::TextOnly;
print '#output: '.UNIVERSAL::isa('Receipt::TextOnly','Receipt')."\n";
print '#output: '.UNIVERSAL::can('Receipt::TextOnly','render')."\n";
#output: 1
#output: CODE(0x84baf38)
[download]

but

use Receipt;
print '#output: '.UNIVERSAL::isa('Receipt::TextOnly','Receipt')."\n";
print '#output: '.UNIVERSAL::can('Receipt::TextOnly','render')."\n";
#output:
#output:
[download]

the second code snippet outputs undef. Back to options 1 or 2.

{::} =D------an (sometimes the cord just doesn't quite reach)