I looked at the textfile2 plugin (only in use, not to edit) and a sample screen. It reads roughly as follows...
id=@01 is text on line one
id=@02 is text on line two
id=@03 is text on line three
id=@04 is text on line four
so the @01,02,03,04 IDs remember what text is entered in the text file for each line,
then these id numbers are called later in the screen to reproduce the text on the module. Something like id 12345678 + 3 more id`s and then increment the id numbers by 1 with each keypress might work. Thus, getting a new id number in a given range, equating to a new line number or set of line numbers further down the page. This depends on how its tied into a plugin though.
To get the keypad (I`d personally use up/down) to work in conjunction with more lines (id=@05,06,07,08 etc) would entail not just a change to the textfile2 plugin but to the keypad plugin too I think. Looking at it their is presently no built in number code to use to indicate a keypress and structure it to pass a call to a plugin. If you want Contrast, Brightness, Winamp, Speedfan control etc then these all presently have built in codes to use with the keypress.
If text wider than the module could be read then thats good, but I think this is going to be asking a lot of a plugin with 4 lines in use on a 20x4 module. Restricting a textfile to 20 characters wide may be the order of the day if this is so. Its possible but a lot of scrolling and a lot of reading on all 4 lines. If it was utilised this way I`d say reserve up/down to scroll through the page. Then use left (line 1), tick (line 2), right (line 3) and x (line 4) to denote lines 1,2,3,4 start/stop scroll. Thats if any of this at all is possible...... the other option is regex-oh please Lord no!!!