Don't think that'll work. Looking at the schematics, it's the very same _RTC_CS that runs to both clockport and trapdoor slot. The battery may be dead on the accelerator but the RTC chip is there and both RTCs will get selected simultaneously, ending you up with random data on the bus.
I'd fix the battery - if possible with a battery holder. If you've got someone with some soldering skills it's a matter of five minutes. Or cut the CS trace on the board. :-/
