Gzip content when using HTTP::respond

I don't think what you're looking for is possible like the way you describe it.

Thinking out loud though, if your content is static you could serve it as a precompressed gzip file? Jason has an article about serving files via ifile here:

 https://community.f5.com/t5/technical-articles/v11-1-external-file-access-from-irules-via-ifiles/ta-p/287683

Oh, and if the content is brotli compatible and the client supports it you migth want to look into that as an alternative to gzip.

https://en.wikipedia.org/wiki/Brotli

Kind regards,
Patrik