1) Find a 4-3 DC or defensive minded HC.
2) Implement 4-3 scheme that stresses assignment discipline and cram your complex genius defenses up your ass.
3) Actually let the talent of the individual players drive the defense instead of trying to make them all jack of all trades.
4) Perry, Clark, Daniels, Lowry with Matthews at MLB. Shake out the SSLB and WSLB with Martinez, Jones, Thomas. I see no issues with the secondary being able to fit into a 4-3 right off the bat play man/zone combo.
Here's another interesting question. Say MM gets the boot and a defensive minded HC is brought in. Would any changes in the offensive scheme really matter with Rodgers in the pocket? Who's your ideal OC?