Something like this is possible, but with a couple of limitations. You are right that you'll need a script for this. It is possible to create a script that pulls all possible approvers of an Approval Request, get the See Also of each possible approver and add them to the Approval Request. A Scheduled Task that runs the script can be executed, say, each 1 hour or something like that to add new if a request has not been processed yet.
However, there can be an issue with groups. What should the script do if an AD group is an approver? An AD group can hold hundreds of users, and each of them can have several users in See Also. This can cause issues. Is such a scenario possible in your environment?
I'd rather use a scheduled task to iterate through pending approvals on a daily basis and find ones that are say 3 days old and THEN send the email more as a reminder.
This is also possible with the help of a script.
We'll help you with the scripts, however we'd like you to clarify the aforementioned issue with groups. What should the script do in that case?