Configure the bolt pretension load to use the Adjustment (displacement) input instead of the Tension Force input. The bolts can move the plate to squeeze the elastomer. In that way, the plate can bulge out between the bolts due to the compression of the elastomer.
Elastomers can cause convergence difficulties because they are nearly incompressible. Using the mixed u-P element formulation for the elastomer elements can improve the convergence. Here are my five must-do items to achieve convergence in hyperelastic material undergoing large deflection.