I have a 10-year old B & D table saw. It appears that the arbor is too
short to add a dado blade. I don't really have the space or budget for
a new saw now.

I'd like to build some bookshelves, and make dados in the side rails for
the shelves. I just finished making a bookshelf where I cut the dados
with a backsaw and straight-edge clamped to the work. It worked well,
but getting uniform depth on the cuts was difficult.

Looking for suggestions on how to cut accurate dados with a dado blade.
For the dados close to the end of the work, I was thinking I could clamp
2 shelf-size boards to the fence before the blade, and use the miter to
cut. Then remove one of the boards and cut again.

Is there a better way?