CPAN::Mini::Inject uses ExtUtils::ModuleMaker, but documentation relating to Module::Builder would also be great.

Module::Build supports this with "auto_features" - see the docs for details. So you might have something in your Build.PL like this (copied from the POD):

my $b = Module::Build->new(
    # ... other stuff here...
    auto_features => {
        signature_support => {
            description => "Module::Signature support",
            requires => q{ Module::Signature >= 0.05 },
        },
    },
);
[download]

and you can then test to see the feature is enabled with $b->feature('signature_support').