Sure. There are a few ways. The most obvious to me, being somewhat of an OO guy, is to modify the functions to become methods - even just package methods. This is as simple as throwing away the first parameter. Then you can do something like this:

my %versions = ( 1 => 'interface1', 2 => 'interface2' );
my $interface = $versions{$version};
$interface->some_func();
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If you can't go and modify the interfaces, perhaps you can play with the imports a bit. This is a bit more dangerous, but probably will work.

my %versions = ( 1 => 'interface1', 2 => 'interface2' );
my $interface = $versions{$version};
$interface->import();
some_func();
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Just realise that the currently-imported version is a global variable (*some_func), with all the repurcussions that implies. You may also get method-redefined messages, although I don't think so, so please test it ;-)