Cutting roots - help a friend

So a guy I know has his girls in 10 litre pots and they are nearly ready for the flip to 12/12 as they are at the perfect height. However his roots are growing out the bottom of his pots - and he is cutting the roots as they do. He is not going to repot at this stage so what can he do apart from trying to coax them back in and hoping for the best - and yes I have advised him about plant shock.

Digitalphd
 
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