Doh! I completely forgot to come back and post to this thread yesterday. I came up with basically the same thing.
edit
/include/client/open.inc.php
circa line 36 through line 38 change
<input type="hidden" name="email" size="25" value="<?=$email?>"><?=$email?>
<?}else {?>
<input type="text" name="email" size="25" value="<?=$info?>">
to
<input type="hidden" name="email" size="25" value="<?=strtolower($email)?>"><?=strtolower($email)?>
<?}else {?>
<input type="text" name="email" size="25" value="<?=strtolower($info)?>">
This makes sure that if they fill out the form wrong, that it echos back the lowercase email address.
Also edit
/include/class.ticket.php
circa line 1131 and 1320 change
',email='.db_input($var).
to
',email='.db_input(strtolower($var)).
This ensures that the email address is lower case when it is injected into the database.
Sorry for the delay.