I don't know if they are available in your area, but CARBONA, the company that used to market carbon tetrachloride for spot removal had a stain remover display in some stores near the detergents a while back. Now you might have to look for it online. They were these little plastic bottles with various potions for removing the type of stain listed on the label, such as fruit juice, clay, etc. There is probably something there for the stains you mention, but the thing that makes perspiration stains difficult to remove is that usually they also have antiperspirant mixed in that was washed into the shirt by the perspiration. Getting the detergent solution past the water repelling mineral salts is the reason why STPP is so good for this type of cleaning. You might try putting each shirt on a flat surface like a half size sheet cake pan so there are sides to hold some water, but do not use a good one for this. Raise the decorative portion on something like a couple of 2 liter soda bottles. Wet the stained area with water then sprinkle a generous amount of STPP and Persil on the stained areas. Use a dripping wet gentle brush to scrub the powders into the fabric. Wear gloves and keep the area being treated wet. Cover the area with plastic and let it sit and keep checking and scrubbing until you see improvement. If you have a rack that you can place over a sink, a dishwasher rack you can turn upside down in the tub or if you can place the item where water can drain through the fabric, you can pour boiling water through the stained area to rinse without harming the decoration. Treating each shirt by hand is going to be a lot more work than just throwing the shirts into a boil wash and you are going to use as much Persil and STPP for each shirt as you were planning to use for the whole load. Even if you could put them through a boil wash, you would need to use more STPP and detergent in the washer to attack the buildup in the shirts. Are they almost stiff in the stained areas? It seems like they could be. I'd check the collars, too. They probably have an oily buildup if these shirts have been so poorly cleaned over the years.
If this is successful, show the shirt to your friend. Ask if he would like to learn how to restore them and show him what is involved. He can decide if it is worth it to him to do it himself or pay you to spend a lot of time and energy doing it. Other than doing this for my own clothes, I would do maybe one for a family member or very good friend and let them take up the task, if they wished.
