The idea that Chareidim are willing to go, en masse, to prison rather than the IDF isn’t just an empty threat; it is the reality.
So round them up and stuff them into prisons in the Negev, feed them slop (with good hashgacha, of course) and put them to work in prison jobs manufacturing license plates or whatever the IDF needs. That is their choice and they understand that for those who engage in civil disobedience, there are likely to be consequences.
The systems cannot survive where the fastest growing segment of the population decides to send everyone else to risk their lives to defend the country while they are paid stipends to stay at home and hide under their shtenders when the air raid sirens go off.