I have a considerable number of access points to convert. All of the access points are new, so they have the MIC from Cisco. So I should be able to just TFTP the image onto the access points, but I can't find any info on this.
This would be considerably faster for me as I could do tens of AP at a time, and I wouldn't have to deal with the rather flaky upgrade tool. Has anyone done this before?
Actually you can do it. The main purpose of the Upgrade tool is to generate a SSC and add the SSC string to the controller. If you already have a MIC, the upgrade tool bypasses the SSC generation process and performs TFTP. You can telnet to an IOS AP and run
"archive download-sw tftp://x.x.x.x/c1240-rcvk9w8-tar.123-11.JX1.tar"
and the IOS based AP when rebooted will load the basic LWAPP code, join the controller and upgrade itself to match the controller's code revision. Now I don't know if this is supported, but your original question pertained to the possibility. So yes it can be done without the upgrade tool provided you have an AP with MIC installed.