The "double" version of the math accumulator instructions are for what you are adding TO the accumulator, not the accumulator value. The accumulator is ALWAYS 32 bits wide.

Hence,

LDD V2000 (some big 4billion number)

ADDB K1 (adds 1 to the 32 bit accumulator)

OUTD V2002 (some big 4billion number, plus 1)

So as long as your K is NOT bigger than KFFFF (i.e. 65535), you should be able to use ADDB (yes, you have to use HEX constant in your BINARY ADD).