DCF in Moscow required actual residency or work visa, a tourist visa did not qualify you to file for it. I knew people who were turned away from DCF because they only had tourist visas.
So I don't know what Warsaw or other embassies would require but tourist visa seems highly unlikely. He should consider contacting the embassies first and seeing if they'll even take someone "living" in Russia on a tourist visa. Since DCF is for "exceptional circumstances" if he's just choosing to stay there as an extended tourist coming in and out, it seems somewhat unlikely they would consider it. However, doesn't hurt to contact and see what they say.