Couple of suggestions

For the nausea ask the Vet to write a script for Zofran. The drug is extremely effective in preventing nausea, and is also very expensive (e.g. 6 doses = $300). The Metoclopromide (Reglan) is usually used in Veterinary medicine because its cost is much less than that of Zofran. It is also no where as effective as Zofran. My Lymphoma puppy got by on Metoclopromide until we ran into a nasty drug at the end, then it was Zofran time. It shut the nausea off immediately. Since the cancer in your puppy has probably spread throughout the GI tract, the Zofran may or may not work. None the less, it's your best try.

Per pain medication, you will have to go with doggy narcotics. All of the common doggy pain medications such as Rimadyl or Deramaxx will make the nausea even worse. In particular Torbutrol is extremely effective. Note the greater the dose needed to suppress the pain, the more groggy the dog will become, unaware of you and its surroundings. But then again this is a very powerful drug, and puppy will feel little pain.