Would "double boiled" linseed oil not do the same? I *think* that Watco is mostly linseed oil, anyway.
The British arsenals used to dip rifle stocks in tubs of near boiling linseed oil. That oil goes nearly all the way through an SMLE stock.
Heating the oil may help get deeper penetration of the arrow shaft.
*The oil is FLAMMABLE! If you do try the heat thing, please take all safety precautions necessary.*
For vacuum pumps, I have read that skateboard shops sell a kit for making custom skateboard decks, and this kit comes with a very good manual vacuum pump.
If you could place your dipping tube in some sort of double boiler, and use that to heat the oil to around 220 F, you should get very good penetration, especially if you also use vacuum.