You would have to upload the speech bubbles for two of the character as an overlay. Have it create with a & before the speech bubble, and then clear it after. So it would look like:
&overlay SPEECH BUBBLE 1 create
&overlay SPEECH BUBBLE 1 opacity 1 in 0
&overlay SPEECH BUBBLE 2 create
&overlay SPEECH BUBBLE 2 opacity 1 in 0
CHARACTER
No!
&overlay SPEECH BUBBLE 1 CLEAR
&overlay SPEECH BUBBLE 2 CLEAR