Personally, I'd braze a hyd fitting to a old grease nipple, make up a hose to your quick couplers and give it some hyd pressure. 2500 psi might do wonders.
If you have to split the tubes to loosen the pins, the cost of professional welding would be less then the new pins you will need if you smash the old ones all up trying to free them.
welding job woul only be 20 to 30 mins.
It would be nice to hook up the aux couplers to the grease nipples but i really doubt the pressure will be there. Most grease guns can do around 10,000 PSI and our little bobs can only do 2,500-3000 PSI.
I'm not sure what pressure the injectors that you hammer will give, but i would suspect it would be more than 10,000 PSI.
It really depends on how much rust you have, if there is a lot no matter how much grease you try and pack in you will never get anywhere.
If you have the gear, i'd try and use a pull ram and weld it to the top of the pin (top of the bobtach) with a piece of pipe over the ram rod to give it something to push against. Pull the ram back to apply pressure trying to draw the pin back. If it will not pull out that way, pull the ram as hard as it can and strike the under side of the pin with a hammer.
I have done this with a small porta power unit to pull pins from my 4 in 1 bucket. I welded a thread the the pin and screwed the ram to it with pipe as a spacer. Pumped the power pack to put as much pressure as i could on the pin to pull it back and hit the other end of the pin. Some were so tight i needed the oxy set to heat it and hit it with a hammer. They all came out!.
Its a shame i don't have pictures as it explains exactly what i mean. Its very simple. Worst case you may be able to hire a porta power setup with a pull ram with an adaptor you can attach to the top of the pin.
You said you have an oxy set, have you tried heating it up? Use a cutting tip, just don't press the oxygen lever. The cutting tips heat large sections far better than the brazing tips do. Try to mainly heat the boss the pins run through instead of the pin.
If you need pics, i can take some of the porta power setup i have just so you know what i'm taking about.