Woah i better lay off the stamps for a while. Seems like life of cheating in neopets is getting harder.
What you got to do is make 1-2 accounts a day, put each of them on different proxies, then do the 40k on each of them once every two days. Once you've got enough nps, send all the money from all the accounts to a newbie account, then self freeze all the old accounts. Then send the money to another newbie account and self freeze the account you sent the money from. Leave it on there for a few days/weeks and then send the nps to your main. Hopefully you will not get frozen with this method.
Probably random? I've AB'd at the stamp shop for about 4 hours on two separate days. Haven't been frozen yet. Made quite a decent profit! Only started main shop abing though.