Bread yeast was originally derived from beer yeast. They are both
Saccharomyces cerevisiae. It could be that your spent yeast are too spent, or it could be that the strains have differentiated so much that the beer yeast isn't adapted for bread raising (though I can't see why not).
In any event, a better idea than recycling spent yeast is recycling spent grain. It makes for a great whole wheat bread. You can see details in the
Bread thread, more specifically starting
at Post 18 with pictures of the process and finished bread and
Post 22 for the recipe and instructions.
Chad