No, there is not a way to do this right now. Think of it this way - all leads receive both versions using the MIME format. Their email viewer is set to read HTML or Text version. Some old clients like PINE will only see the text version. Thus, everyone receives both. I would expect the number of text only viewers to be in the 10% or less range for most businesses. For people like sysadmins or security folks, it's possible this is higher.
If you want to test this, i would create a Text Only email and a regular email, then do a whole email test. I know of pro-bloggers who write only in text or mostly text and it works well. Your audience may feel otherwise.