Use onboard vision system for stabilization and disable the GPS/compass?
If you go into QGC select [vehicle setup]-->[parameters], do a search for EKF2_AID_MASK. It should be 280, which means ignore GPS and only vision is used for positioning (can literally disconnect gps to confirm if you like). This should have been shipped as default since seeker is an indoor mode drone. Turning off the compass is just a couple more parameter settings, but let's go one step at a time.
Beware of your failsafe settings and that vision control requires good lighting conditions. This is a very critical point for [any] VSLAM to work. If there's a vision fault (e.g. bad lighting) the drone will typically drift away from position hold such that you need to put it in manual mode or alt-hold mode to regain proper control. The position control camera is the 45degree down facing camera--hence good ground lighting is desired.
If EKF2_AID_MASK is not 280, cancel out of that and click on parameters again, select [tools] and [load from file] using the indoor parameter file you can get here. If you check the aid-mask parameter again, it'll be 280.