How to tell Final Cut 6 to "send to" Motion 3 instead of Motion 5

Sorry if this has been posted here before, but I'm running Final Cut 6, with both Motion 5 and Motion 3 installed on my machine. They both play nicely for the most part, and I'm just keeping Motion 3 around to roundtrip from Final Cut.

The only thing that doesn't seem to work is as soon as Motion 5 is installed, Final Cut 6 wants to use it as the "send to" option when exporting footage to Motion from the timeline. Is there any way to edit a preference file somewhere to tell Final Cut to use Motion 3 instead? The roundtripping option to Motion 5 results in too many bugs to be useful (for example, the footage doesn't actually appear in Motion, though its layers do appear). Any help around this would be great.

Thanks,
d