Hi Jennifer,
Yes, this can be done. In the email editor, use the Lead Owner's email token. Then, highlight the token, copy, and go the hyperlink functionality of the editor. In the the first line, "Link URL", put "mailto:{{lead.Lead Owner Email Address:default=edit me}}". This will create a hyperlink to email whoever the Lead Owner is. The default will work just the same, so if the Lead does not have a Lead Owner per chance, then the functionality should work just the same with your default value.
Hope that helps!