If you dont want people seeing the txt you are recieving have you tried
Handcent SMS? i know you can add a number to block and it wont show up in the thread as the sms but the txt is there once you unblock it.
the only fallback is that it will go to the orig sms txt app on the phone. i guess you could turn off the notifications to it.
.handcent.com/Faq.php#TAG_USEBLACKLIST
how to add people to unblacklist:
1. check the option ("settings"->"security & privacy"->"show black list" , handcent will ask for password if you set password before)
2. return to handcent main window,you will find the blacklisted thread (people) shown and has grey background
3. long press the thread that you want to unblacklist ,choose "unblacklist" at the context menu