Don't. Whatever remains of legitimate uses of the "reply-to" field only survives as long as it is not conflated with the return address.
RFC3834 gives some recommendations in its section appropriately named section 4. "The Where to send automatic responses (and where not to send them)", e.g.:
Reply-To [..] In general, this field is set by a human sender based on his/her
anticipation of how human recipients will respond to the specific
content of that message.
Towards certain recipients I even deliberately use that field only to be able to clarify in the from header where they can stick useless machine chatter, in cases where the only response I am interested in is one that unambiguously clarifies that an identifiable human has accepted legal responsibility for the matter.