If it is raining, or not very hot, then you can place the flowers on a table in an attic, or in a room that is without a fan or air-conditioning, and the room should be void of dust and sunlight. At the very bottom of the stem, bind the flowers into a makeshift bouquet and tie loosely with string. Don't tie the stems too tight, or use rubber bands, as this will cut into the stem and the flower will begin to decay and discolor too quickly. You will need a room that does not have dust or direct sunlight. For this purpose, I have always used my attic.
Attics are great places, as they tend to be dark, dust-free.
Don't use a basement, as they tend to be damp and humid. You can also use an unused, empty closet. In an attic, you will usually have overhead beams. On the beams, you can hammer nails directly into the beams, and hang the flowers upside down by the string. If you need to use an empty closet, you can hang the flowers from old hangers, or stick-on hooks attached to the walls within the closet.