https-X-Forwarder for MYSQL VIPs - revealing source ips

You could try to insert the client IP into TCP option 28.  This is pretty standard practice for getting original client IP address to a server over non-HTTP protocols.  Some CDN vendors even have a checkbox to enable this for TCP LBs.
You can review this DevCentral article explaining this functionality.  Although, that article is the reverse of your situation; i.e. it is the BIGIP extracting the client IP from TCP option 28, rather than injecting client IP into it.

However, if you do this, then the server will have to have some way of extracting the client IP out of the TCP header.  If that sounds like an option, I can throw together a quick iRule to show you how it would be done.

Another alternative that may or maynot be viable for you, is to move the SQL server "inline" behind the BIGIP.  Meaning the BIGIP ip the default gateway for the SQL server.  This would remove the need for NATing the traffic and the server would just see the original client IP in the IP header.

Hope one of those works for you.

Joe M