Hi Kirk
We done a fair bit of thinking about really similar stuff to the above, and I don't think it's possible. Marketo dedupes email addresses at the send stage, so you can't send multiple emails to the same email address from within a single email program or smart campaign.
So what can you do?
1. Give them access to view emails in Marketo so they can "preview" the email themselves, and check the segments.
2. Create different email programs for each one - basically, the extras are dummys that are only sent to your internal seed list.
3. Send test emails using leads that fall into different segmentations. Still time consuming, but at least you don't need additional programs.
4. Create a smart campaign that send them the email, modifies the field that controls the segmentation, then the next step sends the same email, then change the field again to the next value, send the email again, and so on.
None of these are ideal, I know...but I think those are your options. Good luck!
Phil