So
chewt0y, talking to kovid over
here, he says a series identifier should work with the existing identifier field if you define the identifier in the plugin. I don't know how complex it would be to get the plugin to grab metadata for individual books when using a series identifier, but probably less so than adding a GUI for selecting search results.
Edit: Even grabbing the series metadata would be a useful stopgap, if users just disable filling the "title" field. You don't already have a series identifier defined, do you? Looks like Comic Vine uses "4050" as the series prefix.
Sorry to dominate the thread here for the last little bit, but hopefully it's useful feedback.