I have often just washed the dirt of plants to transplant into a
growing medium for hydroponics. So just planting them in soil until they you are ready is an option. The only downside is that soil born pathogens can be introduced into your
hydroponic system that way. Some plants are more susceptible to that than others, strawberry's are very susceptible to that for instance. But if it is only going to be about a week or so, I often just set the seedlings in coco coir, vermiculite or perlite and hand water with a diluted
nutrient solution. About 1/4 strength every other day, then when the plants get a little bigger and stronger, I'll water with the 1/4 solution every day. Then when they get a little bigger, I'll step it up to 1/2 strength and so on.