Nothing you can do, to my knowledge.
About a year ago, we took in a stray kitten. I scheduled an appointment to have her fixed at the vet. I told my girlfriend "I think we're a little late. She's looking pretty chubby" When I took her in, they said she was pregnant. I told them to abort the kittens (we already had 8 cats) and have her fixed when done. They told me "she'll be ready at about 2pm. We'll call you before then if there's any issues".
At 1:55pm I'm getting ready to call the vet when the phone rings. It's the vet and I'm thinking they are calling to tell me she's ready to come pick up. But...NO, they call me to tell me she tested positive for FIV. Well, with 8 other cats we had to put her down.
It was devastating. My girlfriend cried for a week and a half. I was NOT happy with the vet. They could've called at about 10am to let us know but they let us think everything was alright and then hit us with the news right when she's supposed to be ready to get picked up.
If they are diagnosed with this, you pretty much have to put them down if you have other cats. They pass it through bites and saliva at food dishes.
Sorry for the loss. Pets, to me, are like family members and it hurts to lose one.
EDIT: Our vet told us it could be passed at the food dish although this link says nothing about it...
http://www.vet.cornell.edu/fhc/brochures/fiv.html