Adding an Accumulator / Kalman Filter to Optical Flow Tracking Model in Simulink

Hello,

I am having some trouble adding an accumulator to the tracking algorithm I am working with. The model adds a bounded box around targets based on their blob size - I want to only add the boxes to targets with a steady return, thus eliminating any false returns. My thoughts drifted to placing a Kalman Filter in the model but I can't seem to get the block in Simulink to work with the existing model (below):

Any help in solving this problem would be greatly appreciated!

Many thanks,

Chris