Several players have suggested work-arounds. You can create a second message window tab for the System messages (including the kill messages), and drag that tab to create a second window. Then use the Message Window Size (tilde) key command to toggle the size of the windows. I have a controller button mapped to toggle window size.
I have two windows, one that normally shows two lines of System messages and one that shows 4 lines of all other messages. Both expand to 10 lines using the window size toggle. This allows me to read Country channel messages without kill messages scrolling past, and expand the System messages when I need to see 'object destroyed', salvo, etc.