Anything can be used as a warping board. You can wind warp around a building if you have to!
Here are some other suggestions: the legs of a chairs turned on their backs, sticks poking out between books on a book shelf, the stems of quick grip clamps, or an inkle loom. As long as you have something at the end that you can wrap the yarn around to make a cross is good enough to be used as a warping board.
Here, someone used the legs of an ironing board to make a warp for backstrap weaving (which you can use with a rigid heddle)
Here's a warping board I made using clamps, pegs and a bookshelf: