4 ads in a mail for example.

1) Set up or send 3 ads for 1 time, either solo or shared.

2) Go to "Mailer Settings", "Create New Set"

List your 3 ads in Email header,

3) When sending the 4th ad, just choose this Header Set. You may then schedule however this email to be sent automatically.

This method may be used for various ads good for whatever amount of clicks. You just need to remove the expired one from header in the future.