Not without getting Keltec to redesign the RFB.
When the RFB was first shown, metric FAL mags where much closer in price to G3 mags, but they've gone way up in price during the intervening years. Just keep an eye out and you can find them for around $15 on occasion. And there are some projects to start making new polymer P-Mag type FAL mags, which should increase supply.