2 lines dropdown menu "word" style option

i have 2 dropdown menus lines

line1 and line 2.

my code is :

keystroke script :

var desiredLength = 5; // the number of digits the user should enter

event.rc = true;

if (event.value && event.value.length>=desiredLength)

{

    event.rc = false;

    getField("line2").setFocus();

    this.getField("line2").value = event.value && event.value.length;

}

if (event.value && event.value.length<desiredLength)

{

event.rc = true;

getField("line2").setFocus();

}

now i want when line 1 is full length characters then go my letters on line 2.

eg:

[line1]1234567               <------ i put this with my keyboard

[line2]67                         <------and i want to move automatically the characters > 5 in line 2

it is possible ?