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.