Using a single pole crossover such as this might pose a danger to the tweeter if it cannot handle the lower frequencies that would be passed by a 6db per octave crossover. If I were going to use the passive route (I actually do for my front center speaker, before the power amps) I would use a two pole inductor/capacitor/resistor filter which would yield a slope of 12db per octave, which is probably the same as that in the speaker's passive crossover.

In any event, I agree with Charlie on this however. It's a simple matter for me to fashon a line level LCR passive network, but It's probably beyond the capabilities of most HT hobbiests. I would recommend just going the full electronic crossover route. This would yield the benefit of being able to select the crossover point to achieve best response.