You can probably acheive this by altering the symbol table:

package Bar;
sub import { print "Hi!\n"; }

package main;
use warnings;
use strict;

BEGIN{*{Foo::} = *{Bar::};}
# can't "use" there because there is no Foo.pm
Foo::->import;
__END__
Hi!
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Write a header in your script that once uses Coro::Socket and then replaces IO::Socket::INET:: namespace with Coro::Socket::. Subsequent uses of IO::Socket::INET will call import() from Coro::Socket and will use its subroutines.

Edit: you'll probably need to use IO::Socket::INET before replacing namespaces, too, so further calls to it won't eval it and overwrite Coro::Socket's subs back.