Leverage your position over the saddle and thrust your hips slightly back and under you to offload some work from your quads to your glutes to target your glutes while cycling. Shorter periods of standing while pedalling can also assist in glute muscle activation. Once they are active, lower back down into the saddle and continuously attempt to hold onto that throughout the exercise. This is very beneficial when you are in an aero position and you feel that your quads are overworked. Do this on a trainer first, so that you are able to feel what it feels like then perform it on the road when in high cycling intensity.