Alternative Plain Text in Email Messages (multipart)

Hi,
I have the following situation: in a CX project, we send invitations for a NPS survey to customers via an Email action in Qualtrics. The email template is maintained as an email invite in the message library and contains the NPS scale question. As far as I can see in the source of an sent email, it is sent as multiplart email, containing an alternative plain text representation that is displayed in case the email client does not support HTML/CSS representation of the mail.
The plain text simply represents the numerical scale:
Very unlikelyMost likely                         
0 1 2 3 4 5 6 7 8 9 10 
We would prefer to show the URL of the survey instead. Is there any way to change / adjust the plain text version of the email template?
Thanks for your help!
Regards,
Jakob