The Lua side of dialogs is pretty much non-existent.
You could consider using some conditions / values & creating a called by other action which checks the value of a value which you increase / decrease at the end of each selected dialog part & if the value equals a specific value then check which condition is still true & display the text for that & then end the dialog. Sorry for being a bit vague, but I hate the built-in dialog system - it's not very flexible.
* edit #1: there is something else you could potentially try but I don't think anyone playing your game would appreciate it very much as it involves taking control of the mouse & forcing it to move or jump to a specific position on the screen, then creating a temporary left click event.
if Values["test"].Int == 0 then
setCursorPos( { x = 500, y = 500 } ) -- update cursor position
createEvent('eEvtMouseLeftButtonDown'); createEvent('eEvtMouseLeftButtonUp') -- create left mouse button pressed & released event
end
I have no idea if this would work & it's a shitty hack-job either way!
* edit #2: figuring out the x, y position would be fairly easy & should remain consistent throughout each dialog. Run your game, get to a dialog part & run through them until only the last one is left (though technically it should be in same position as the first dialog I think) then hover your mouse cursor over it somewhere so that it highlights it (preferably somewhere near the beginning of the line) & then press TAB key to open up the developer console & type...
exec print( getCursorPos().x, getCursorPos().y ) then press enter, now do the same again except type
PRINT LOG & then press enter to display the log. Now look for the values it printed & make a note of them.