Eggdrop is designed to follow the IRC RFC.
This defines the rules, that are needed to support basic IRC services.
The k mode is not a stardard mode, as defined by the RFC, nor is the method of messaging him.
As this breaks the rules of the RFC, it's doubtful it would be supported.
However, you can subscribe to the eggheads.org mailing list see the
eggheads.org site), and submit such requests there.
Stating the full ifnrmation regarding the nature of the usermode, and how it affects messaging.