When you post your ad tell them what you know. That they are extras the hatchery sent you for warmth & protection. They are purebred somethings -- the hatchery may be able to tell you, or post pictures here & other folks can guess. That they are most likely to be roosters, the hatcheries typically use them for packing peanuts because that's what they have the most of to spare. However, the hatcheries can have up to a 10% margin of error in their sexing, so there is a slight chance there is a pullet there. This is different from straight run, where chicks are selected from a group that has not been sexed, and you hope for around a 50-50 split of sexes.
If you advertise them as straight run folks wanting a fairly even division of pullets & cockerels will be disappointed if they all turn out to be roos. If you advertise them as what they are, you should still find folks who want them, but will know what they're getting & why.
Last summer I was grateful to be given 2 different batches of packing peanuts from other folks' hatchery orders. They were SLWs & RIRs. A few went to other folks who wanted those breeds of roosters to husband their hens. The rest came in for dinner with my family, a worthy purpose.