Client Source IP - SSL pass through

You could, in theory, utilize Proxy SSL, assuming your security policy allows it. This requires that you have the same SSL cert and key on all the pool members and that cert/key is available to the F5 as well.

https://support.f5.com/kb/en-us/solutions/public/13000/300/sol13385.html

With this configuration you can use an iRule to insert/modify X-Forwarded-For.

This is, for all intents and purposes, doing a man in the middle. It only works for RSA. If you require ECC it doesn't work.