If they're asiatics - perhaps not much. Mine have been above ground since last month and I've had frosts plus low night temps. (I know! Nothing like yours.) They're fine down to -3C or a brief burst of -5C - and they keep on growing. ('Brief' means frost overnight and gone before lunchtime.)

Can your friend bring them into more light rather than slowing them down?

About the only other lily I have showing at present is a little martagon. Just first leaves so far. The rest are still below ground.

As your planting season isn't until May/June - would a change to oriental lilies be an option? Later to rise - and they smell delicious.

Are they Asiatics or Orientals?
Asiatics will survive in the ground in zone 3. I am in Zone 1(-50 below) and mine survive. Some are 5 or 6 years old and have to be divided.

Orientals won't survive in the ground but after 5 years of storing them indoors, I've not found anything that will slow them down when they are ready to grow. I unpot mine and store in a designated "bulb refrigerator". Initially I put them in in late September at about 40ish degrees because I was also storing other bulbs. They started growing in February. Last year I stalled putting them in the fridge till October at about 33-35 degrees (later and cooler), they still start growing in the fridge in February. I don't know how the growers keep them from sprouting, but mine wake when they are ready and you can't stop or slow them down.

If your friend is storing them at 48 degrees, I'd suggest cooler temps to see if that buys him another month or so.

I'll pass the information along. Thanks.