It's been awhile since I looked into filters and crossovers, but can't you use an ?active? filter (I think its called active, it's the filter that's used after the signal has been amplified). You'll lose a lot of power this way, but atleast you have some control over the frequencies going to each speaker
IIRC you should be able to just use an inductor on the woofer and a cap on the mid range. It won't sound that great, but it's a start.
I think I searched for DIY and crossover, there's a whole bunch of info on this.