It seems like DBM provides respawn timers on the trash in Karazhan and it is enough of a feature that I want at least one raid member to have DBM. Is there any way that could be incorporated into BigWigs?
DBM doesn't have trash respawn timers, the timers you got were most likely custom timers from one of your raid members, you can make custom timers in BigWigs quite easily.
You can download Incubator which is a trash respawn timer addon.
When fighting the Curator you will be told that the Curator will get into his mana regeneration phase in about 70 seconds.
Maybe it would be possible to change that into messaging a 60 seconds range (or add an alternative message). This way warlocks could time their curse of doom better which will explode after 60 seconds and thus doing its damage in the regeneration phase.
They should just get BW themselves and time it with the bars.