Can you get hold of a cytofuge?  Hematology departments often have them.  To centrifuge a cell suspension on to a glass slide.  You can use polylysine-coated slides to make the cells adhere, and then fix them with the specified fixative, or fix them in suspension before spinning (then you can spin harder).  Then you can go through the staining and washing steps very easily, much as for a tissue section.   I think dead cells do not pellet very easily, somehow they are not as dense as live cells, so you would also bias your counts by repeated centrifuging. We had the same problem and moved to this cytofuge method.  You also need fewer cells.

Dr. Bennett's suggestion is good for microscopy. For fluorescent TUNEL by FACS still you will have to use cell suspension. Apoptotic cells tends to disintegrate when repeatedly centrifuged. I reduce this loss by adding 1% BSA in PBS for washes (PS: it wont prevent loss..but reduce it) and increasing starting material. Also add an unstained control with BSA+PBS wash to set gates. BSA increases auto-fluorescence.

Thank you for the suggestions