I would certainly recommend what Tim has suggested, and that is bleach the areas that are almost impossible to 'hold back' during printing.

For this I favour an iodine bleacher over ferri.

Iodine Bleacher for prints:

iodine 4 gm.
potassium iodine 15 gm.
water to make up to 1 litre.

Remove the brown iodine stain with 30% sodium thiosulphate (hypo) solution.

Wash print well.

This stock solution keeps for years.

You can always dilute the iodine solution further if it is too active.

For lightening small areas I apply using cotton buds. When the desired result is achieved swob the area with the 'hypo', then wash print well. Practice on spare prints.