Give the CS anally with a baby rectal syringe. Tony Isaacs (aka Dquixote1217) has a forum "Ask Tony Isaacs", would be able to give you some guidance. Here is the link that he often posts for cancer in animals.
Oleander might be of use here, but only if it can be given rectally**** (email Tony to find out first. Utopia-Silver has Oleander capsules that would be helpful for this, but only if it is ok. I seem to remember reading that Tony said rectally would be ok). Orally, it upsets cats (and dogs) tummies so much that it comes right back up. IP-6 inositol hexaphosphate supplement has tumor fighting properties too,.