I would suggest getting some of those cheap little plastic scrubby pads from the dollar store or cleaning section of the grocery store and some smallish 2-4 inches river stones, that are typically used for decorating the floor of the tank, the scrubby pads are open woven for water circulation but dense enough for fry to not just wander in.
Figure how to set the scrubby pads over the grate side by side. You could even sew them together horizontally if you aren't scared of a needle and thread, lol to keep them together. Lay the stones over on top of the scrubby pad and pile them up a little if necessary to weight them down.
The reason for the plastic scrubby is to maintain space under the rocks for the water circulation, if you just used bulk filter pad it might crush reducing the circulation too much. Although you might be able to double or triple lay it if you can't find the scrubbies.
You want to get the water circulation back on asap to keep your bb alive if you have any other stones or media in the filter area.
I am not specifically aware of how the media area is in your tank.
Congrats!!! And just a word, you are doing well to save some babies, and the fish will likely have more babies in the future and you can be better prepared if you know they are coming!!!