It could only be increased by modifying the underlying data model (which I'm not suggesting you do). Why don't you just utilise Integration Option2, 3 & 4 to store additional emails or better still create an email group with all the recipients you require in your email system and mail to that, keeping the management of email addressess in that system
Yes, we do have workarounds for this issue. Probably we will put the email id's in a file and read from there.
I would create a dummy location for maintaining email addresses.
You can use any of the dimension mapping tables. For example:
It's better for maintenance. Then you can easily build the to_addresses by querying the mapping table through the script.