question
Can you take a pic of it and show it to us. I am at a loss on exactly what it is that you are referring to. Most of the time, the screws will thread up into the receiver itself. At times, there is a base that is welded or soldered on, maybe this is what you are referring to. If it is, then yes, it can be soldered back on, but like I warned you about, you have to know how to control the heat and localize it to prevent causing problems up the receiver.
Let me tell you something about guns. Most are in the 40,000psi pressure range if they are a centerfire rifle. That my friend is enough to cause the action to split and come apart in various pieces at a high rate of speed that can blind and or kill someone, so even if it is just at the back of the receiver, don't just go to welding on it. Heat can and will travel up and down the receiver and ruin the tempering of the steel which is why I warned you about it. There are a lot of things that have to be taken into consideration when something is broke on a receiver and needs to be reattached. You can take that for what it is worth to you.
I would rather you take it to a smith and let him atleast tell you what he thinks needs to be done to the gun. Heat paste as well as wet rags can be used to control the heat, but you need to know what you are doing when it comes down to it. Best of luck with fixing the problem. I know you need to get it fixed and reattach the stock to the gun.