If you have access to the serial-console of the IAP you can also try:
1) Connect serial console
2) Power up AP
3) Press <ENTER> to interupt the boot (and enter AP-boot)
4) For AP-105, type: upgrade os 1.1.1.1:mips32.ari (where 1.1.1.1 is the IP of the controller)
5) After the image is loaded, type: boot
For this to work TFTP should be allowed towards the controller.
The AP should fine the controller, presuming the AP is either in the same L2 domain as the controller or if a DNS record for "aruba-master.DNS-SUFFIX" is present. If not available you could set a variable for the controller via "setenv master 1.1.1.1" in AP-boot.