using spiced pumpkin

I am wanting to put spiced pumpkin in my milk stout. I brewed this weekend 11/2. I was planning on putting it in my secondary but Im not sure on how much or how. I don't want it to spicy just enough that u can slightly taste it. I was told that I could just go to the store and get some spiced pumpkin and put a little in some vodka and put it in. im just not sure how much. im just wondering if anyone on here has done it this way or the way they did it.