Note that bakelite is a thermoset polymer, not a thermoplastic polymer. A thermoset polymer is one that hardens/cures when heated intially and then does not soften when heated again, unlike the more common thermoplastics (e.g., PET, polyethylene, and most other common consumer plastics), which will soften and melt when heated again. Bakelite will still decompose if heated too much. From what I've read, Bakelite will start to decompose around 300 F, but will probably be OK up to around 350 F (it's a phenolic plastic, which are generally considered oven safe to 350 F).
That said, if I were going to season it, I would probably go low and slow (250 F - 300 F) and bake it for longer than normal. The vegetable oil will still polymerize at a lower temperature, it will just take longer, and the resulting polymer may have a slightly different structure than one made at a higher temperature. Alternatively, you could use a grill and leave the handles sticking out in the air so they don't heat up.
(And yes, I work for a major specialty plastics company and have experience in polymer chemistry.)
Edit: I just noticed that Russell posted the grill idea. I think that's where I saw it originally.
