Hi Kendal,
good question! I had the same issue and I resolved it as follows.
Let's say you have three e-mails linking to whitepapers on your website. Leads can request all of them through a form fill out that will send the e-mail with the link to the whitepaper. You build 3 programs, one for each whitepaper. Within those programs you will have (at least) 2 smart campaigns, one adding leads to the engagement stream (using the "member of engagement program" filter) and one sending the email to the lead straight away (using the "fills out form" trigger). Because you will use the same e-mail with link to the whitepaper in both smart campaigns, the lead will receive the requested whitepaper straight away and he won't receive it again thourgh the engagement stream because he already received that e-mail.
Does this make any sense?
Cheers,