Redefining myhosname to a location outside of main.cf

[VR]

On a test box in Postfix 2.5.5 I tried putting myhost.domain.tld in 
/etc/postfix/myhostname.cf and then defined myhostname = 
/etc/postfix/myhostname.cf in main.cf.

Since this does not work, is there an available option to move 
myhostname out of main.cf and into another file name or type?