It should be possible to install without replacing bootloader. Try that on one of your other units.
It may be necessary to unsolder the flash chip to get a good write. With OpenWrt running you can read the bootloader out of an unmodified unit.
Yer i saw this but to me this as an IAP-105. In the UK we have the IAP-105 that has GUI interface and can be a controller where the AP-105 is dumb and needs a controller to work.
I have tried the TFTP method but cant seem to get it do boot to TFTP
Does it look like the IAP-105 is the same hardware?
If the bootloader is the same the netget command should work to TFTP to RAM. Problems with TFTP booting are almost always on the server side, for example not disabling the machine's firewall.