Fast Failover seems like it only helps if the AP has already successfully booted from an active Master controller. That doesn't address bootstrap failover at all.
They way I see it -- and someone please chime in if I'm wrong, because I probably am -- you have two options for boot-time failover:
1) Use VRRP between two controllers in a layer-2 domain. They may as well be in an HA group as well, so you also get Master role redundancy. You can assign this VRRP IP to the LMS field in the profile, as a DHCP option, as a DNS A record for "aruba-master", or leave it to ADP to discover.
2) Use LMS / Backup-LMS to point to two different controller IPs.
I've been testing the latter option, and so far it doesn't seem to work ... at all. If the AP's home controller goes away (pull the data cable), the AP shuts down the radios, and the power LED blinks. It does this for about a minute or two, then reboots. At this point, it can't find its controller via ADP (the BLMS is a few layer-3 hops away in my case), and just reboots itself perpetually.
So, when exactly is the BLMS IP supposed to kick in? It doesn't seem like the AP-105 bothers to attempt to connect to the backup controller after losing connectivity to its home controller. It just waits for a while, then reboots. And then, it doesn't have the BLMS setting in memory anymore.
DHCP option 43 apparently only supports one IP, so that's no good. You would ordinarily want it to go to the local controller.
DNS supports multiple IPs, but is the order deterministic? I.e., if I assign multiple A records with my preferred controller and at least one backup, how do I know it's going to try the preferred IP first? Also, that doesn't seem to be a reasonable option when you have multiple sites, and want to give the local controller first dibs at each site. That would require per-site DNS entries. Wouldn't you normally just have, for e.g., a central AD server for internal DNS?