The cheap but punctuation-heavy answer:

my $string = "this is an interpolated method call: @{[$obj->method]}";
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What's happening here, working from the inside out:

1. The method call happens, and it returns a list of zero or more values.
2. Outside that, we have an anonymous array constructor, so now we've got a reference to an anonymous array containing the value(s) returned from the method.
3. Outside that, we have @{ }, which dereferences the array reference, so we have an array.
4. Perl now happily interpolates the dynamically-generated anonymous array into the string, because it knows how to do that.

This is essentially what Interpolation.pm does, cut down to adding a few extra characters in your string. Drawback: ugly, and possibly really confusing to the reader. Advantage: only 5 extra characters.