sealing track bike hubs?

'Sealed' bearing hubs have a cartridge bearing that can be serviced to a degree (as above) but generally you would just pop the bearing out and replace it. This type has a shoulder on the axle that the bearing sits against and cone nuts and locknuts to keep everything together.

'Open' or 'loose' bearing hubs have ball bearings which might be in a cage but are not in a cartridge. This type has cones that are tightened to correctly preload the bearings and locknuts to retain this preload. There may be rubber seals (see Shinano mtb hubs) or metal shields to keep out the water and grit or not (see Dura Ace track hubs).

The hubs you have are 'sealed' or cartridge bearing hubs.

The only non-bodgy things you can do to further protect the bearings would be to apply a smear of grease (or Vaseline) to the outside of the bearing or to buy bearing cartridges with better seals (your hubs probably already have rubber shielded bearing cartridges fitted so your only hope would be a better quality of bearing/seal).

Here's a pic of sealed or cartridge bearings with the rubber seals fitted and removed -

As you can see you could flush it with degreaser and relube it but you could not actually get the ball bearings out.