Changing "rel" of 301 redirect

Hi!

I've got some questions about 301 redirects. 

I'm currently working on an affiliate website and as we know you should set the "rel" of an 
affiliate link to "sponsored" for SEO purposes. Since I want to use an affiliate link multiple times
on my website I have made a 301 redirect from a sub-domain to an affiliate link. 

An example of one of the redirects I have made:
www.mydomain.com/r/randompage --> johndoeaffiliate.com/r/JohnDoe

The latter link is the affiliate link. 
Now to the question. The 301 redirect works fine, but the URL mapping tool won't allow me to 
write any real code which means I can't use an a-tag to change the rel of the affiliate link. How would I go 
about setting the rel of my affiliate link?