I've achieved this in two ways, but first a caveat: we use RTF formatting so when we call a streamed output report, we send it via the AmyUni RTF driver to produce some formatted output in a .RTF file...

1) With an FRX it's easy. In the EXPR field of the FRX with OBJTYPE=53, you just put a DEFAULTSOURCE= line, then the bin number.
2) With the RTF file, I insert a \sectd section definition identifier, if it isn't there already, then put a \binfsxnX for the first page bin, and a \binsxnX for the other pages bin, and thats it.

Setting the default printer is something I've tried to avoid when interrogating the drivers, but so far have failed with. On 2000 and XP it's fairly easy, but we have some clients on Windows 98 and that's a problem. You don't need to change default printer to change tray of course.

The code I have to detect paper bins also get's fooled sometimes by the printer driver and returns paper types as well. This happens more with HP drivers. In that case, selecting "Labels" just has the printer display a message: "Load LABELS...etc" - it works but it's something to be aware of.

I'll happily post the code if you need it.

Regards
Simon