I see that the LTC2662 can be daisy-chained by connecting the SDO pin to the next device's SDI pin. However, I don't see any mention of the maximum number of daisy-chained devices in the datasheet.
I require 40 LTC2662 devices. Is it possible (advisable) to connect this many in daisy-chain formation? If no, what is the recommended method?
Yes, you should be able to daisy chain 40 devices, each device just drives the next device, so it should be possible to daisy chain an infinite number of devices.