There is nothing you can use - the fleece needs to be changed if it is soiled and smelling. Trying to make it go longer between washes isn’t feasible.
Fleece can be need to be changed anywhere from every 3-7 days but it depends on the set up, cage size etc (the smaller the cage, the more often it can need to be changed).
If he is suffering with bumblefoot then you need to be changing the fleece out probably a couple of times a day until he heals. You can’t risk there being any damp patches of bedding which will make the bumblefoot worse.
Using smaller fleece pee pads can help. Put them on top of fleece but in high traffic areas such as hides etc. They can be removed a couple of Times a day without having the change the whole fleece.
Is the fleece definitely wicking properly?
Piggies can’t be litter trained, so they will still pee and poop everywhere.
Also, there is the fact that boars will scent mark which will make a smell. If you change it all out in one go, then they will scent mark more, so it can be advisable to change half the cage at a time (ie have two smaller pieces of fleece to cover the whole cover) or rub the new fleece with the soiled fleece to transfer scents and hopefully make them feel more at home.