Ok, you can't specify which module to load via @ARGV with use. use basically works its magic at compile time, and has already done its thing before $ARGV[0] is ever determined.

No, not at all. @ARGV is available at compile time, and Perl is capable of executing expressions such as $ARGV[0] at compile time. The problem is that use expects a bareword for argument, not an expression. The generic workarounds (eval "use $ARGV[0]" and converting from namespace to filename for require) have already been posted.