The best way to discourage regression is to not take home a baby until its been a few weeks since its last hand-feeding. A baby can be weaned and fine at the breeders but as soon as it goes to the new home, it starts having problems because of the stress. If you are concerned about regression, give it back to the breeder and tell them you'll pick it up when it's more solidly weaned.
If that isn't an option, you can also give it warm mashy food like cooked soft sweet potatoes a couple times a day. Some people like to give an evening hand-feeding for a couple days and then phase it out. What you do NOT want to do is start giving it a whole bunch of formula and let it con you into thinking it needs comfort feedings 4 times a day. Then YOU will have regressed your baby. If it was weaned, it should be able to get by with either no hand-feeding, or a few cc's before bedtime. Plus some warm soft veggies in the morning and that should be it. Note, that that means about two warm mushy feedings a day: veggies in the morning and maybe/maybe not formula in the evening. This does not mean constantly giving it warm food all day long trying to prevent regression because if you do that, you will succeed in making the baby think that it doesn't need adult food and you will have encouraged the baby to regress. If it needs more than that to maintain weight, you should take it back to the breeder. Another thing that helps is NOT to stand around staring at the baby willing it to eat. Or sit with it so hoping that it'll eat something that you hand it food constantly. Put food in the bowl and then leave. Maybe hand it a piece to get it interested and then leave. Even if the baby drops the piece you gave it and begs from you, you still leave. If you can't keep from obsessing over it, go fishing, take a hike, shopping with your bff, do something that gets you away from the house for several hours. Let the bird learn that its okay to be a grown up. Weigh the bird every morning before the first meal but know that the first day it will lose A LOT of weight. Just the nature of going to someone else's home will cause a baby or even adults to drop weight. This does not mean that the baby has regressed and needs continual comfort feedings. It just means it switched homes and weight loss happens. Day 2 in its new home should have less weight loss but possibly still a slight drop from day 1. By day 3, things should be leveling off(not gaining, just failing to lose more). If not, you need to consider going back to the breeder. Especially if you are doing a once a day comfort feeding and the bird is continuing to drop weight after day 3. It will probably take a few weeks for the baby to regain the weight it lost from switching homes. This is not a weaning issue that necessitates comfort feedings. Even older birds that have been weaned for 20 years will do this. Often times taking a few months to gain back weight it lost in the first 24 hours in a new home.
As you can probably tell, I much prefer that people just leave the bird at the breeder. I don't like people comfort feeding babies that I sell based on advice from the internet experts. People can screw up their bird and make it co-dependent trying to abundance wean their bird. This bird should already be weaned. Abundance weaning has already happened and is done. Giving the baby a bunch of "comfort" feedings that it doesn't really need just fosters co-dependence and all the stuff you don't want. Babies that can't handle switching homes aren't weaned and need to go back to the breeder to grow up some more. That is the breeder's job. Also, when in doubt, discuss with your breeder and consider their advice as more important than that of some random person on the internet.
