Friend of mine has done this on his 306 diesel, and it works most of the time. You can adjust the time it sits with the ignition on and so vary the time that the glow-plugs have to warm up. I think his is set 15 secs and like I said that works most of the time!
He uses the Clifford Concept 300 alarm with the "itellistart" add on. It's quite expensive but it's probably worth it!