I just drag my RTF files directly onto the Reader's entry in the ConnSoft-- I haven't ever tried letting Connect use Word to convert .DOCs to .RTFs.
I don't know of any trick, per se, and I've only had one or two hangs in ... what? ~4 months? I've been handling them mostly through WordPad to keep the file sizes under control, and the only other thing I do consistently is edit them in NotePad and manually add meta-data, but I wouldn't think that would have any effect.
I know
that's not much help to you, but I have seen some indications that the update should make some improvement of RTF handling, so there's a bit of hope there.
Maybe somebody else knows a way to make RTFs more agreeable to ConnSoft that I've not noticed?