I want to use AMember to have people purchase WordPress plugins and themes. However, I want to sell different prices for single domain vs. letting them install like 5-domain packs (and multiples of those). One would go through the AMember workflow to purchase something, and then receive a serial number based on their purchase. They activate the theme or plugin and then put in this serial number in an options panel, and they're off and running with a functioning plugin or theme.
What is the most efficient way to tweak the programming of AMember to accommodate per-domain installations of stuff sold through AMember?
For instance, I was thinking perhaps I need to use this Add Field feature, but then use custom programming against that field.