Can I create a task in Dynamics CRM based on the MSI user triggering the event?

Our pipeline developers and Account Managers may work on contacts they don't own, but are part of a team. Consequently, these reps may use MSI to send an email to contacts owned by several different reps. Additionally, we track our PD/AM activity in CRM based on completed tasks, and often associate those tasks to a particular campaign. This allows us to report on activity of PD aligned to specific campaigns.

Marketo allows me to create a task, but as far as I can tell those tasks can only be assigned to the owner of the lead, contact or account, or a specific user. I haven't been able to find a way to create the task and assign it to the MSI user that sends an email, based on who sent that email. 

The only solution I've found is to create a separate email for each MSI user (which I've already done so we have customized signatures) and then create a smart campaign that looks for a sales email sent with the constraint for "Sent by". I've tested it and this will work, but it's not very scalable. 

Any advice here would be helpful.