Thanks for your replies.
Ken, thanks for the offer, I can make the cables myself (need 6 of them), I was just wondering if there was an easy way to go about it. As I said, a field configurable modular plug with shorting bars would be perfect, if it existed.
bfdatacom, your suggestion makes sense, but the connection is UTP/RJ45 all the way through (enviromental sensor to serial-to- ethernet device). After a lot of asking around, I realized the wiring was not the standard EIA/TIA 561: RS232 Over RJ45 but a so-called Yost wiring: Yost serial
The manufacturer of the sensors suggested a null modem cable with partial handshake as in this page: Scroll to partial handshake . I'm trying to do it nice and not go the bulky adapter route. How do you short RJ45 pins in a proper way? It's much harder than I thought.
Arthur, thanks for the info and the humor. I was thinking about the dual jack option myself or maybe a splice box? As for the KS 19252 adapters, they're proving very hard to find! A couple of places I called were more interested in buying them from me. They would work, I'm sure, but I've already ordered the AMP wear adapter as well as this and I'll give it a go.
And then as hbiss suggested there's always the 66 block option with amphenol in/out. That's the easiest, and I agree it would make much more sense to begin with. It never ceases to amaze me when people are duped into going for something that is not only more expensive but also less flexible. It looks good in the rack, I guess.

PS I'm writing this on a new Apple Air notebook at the apple Store here in NYC. Very sleek, I came in here on my way to work looking for a likely post-Christmas purchase (when prices come down a bit). It definitely's got the looks, I'm putting it through paces to see how well it works. Not very cheap compared to Windows notebooks.