That's a very nice method, Dave. It won't accommodate a comma, question mark, or any character with more than five elements, but you probably don't need those characters in that application.

One method I've used involves inserting a single '1' bit terminator after the last element. This allows for characters or pro-signs up to seven elements in length and eliminates the need for an element counter. A space character is empty except for the terminator bit ('10000000'). Processing the dits and dahs is similar to the method in Dave's example.

Code:
id
        retlw   b'10010000'     ; 'd', dah-di-dit
        retlw   b'01000000'     ; 'e', dit
        retlw   b'10000000'     ; ' ', space
        retlw   b'10110000'     ; 'k', dah-di-dah
        retlw   b'11100100'     ; '8', dah-dah-dah-di-dit
        retlw   b'01001000'     ; 'l', di-dah-di-dit
        retlw   b'00001000'     ; 'h', di-di-di-dit
        retlw   b'10010100'     ; '/', dah-di-di-dah-dit
        retlw   b'01010000'     ; 'r', di-dah-dit
        retlw   0               ; end-of-table