Currently Marketo provides tokens for Account Owner and Lead Owner, but not Email Sender. Some Marketing Automation systems provide this, so that you don't have the awkward situation where an inside rep sends an MSI email to his field rep's lead, but the email template merges the name of the lead owner into the email, rather than the sender.
To avoid this, we've had to create smart campaigns and flag fields that temporarily change the lead owner to the inside sales rep during an inside sales campaign.
The best way to handle this is a token that references who is sending the email and merges - please add this.