You could theoretically use a custom force law - and you should be able to turn it on and off.
See this submission: https://www.mathworks.com/matlabcentral/fileexchange/109680-multibody-contact-force-block-examples-in-simscape-multibody
In particular this example in that submission: https://www.mathworks.com/matlabcentral/fileexchange/109680-multibody-contact-force-block-examples-in-simscape-multibody - Note I have not tested this with negative force values, but I believe it would be possible
You should also have a second Spatial Contact force block that prevents penetration into the solid (Or if you create your custom force law to do this you could possibly create something that is computationally more efficient).
You could also make use of the External Force & Torque block - https://www.mathworks.com/help/sm/ref/externalforceandtorque.html?searchHighlight=external+force+block&s_tid=srchtitle_support_results_1_external+force+block - based the force on the Magnetic attraction force equations, and use the seperation distance output from the Spatial contact force block to measure the distance between the two bodies.
