Finding a reduction for two-Subset sum problem I'd like to prove that the following problem is NP-complete. I'd just like to know what reduction I should do:

Two Subset Sum: Given a set S of integers and an integer T, determine whether there are two subsets of S such that the sum of the numbers of one is T and the other is 2T. The subsets do NOT have to be disjoint.

And I want to use the classic subset problem to prove this:

Subset Sum: Given a set S of integers and an integer T, determine whether there is a subset of S such that the sum of the numbers is T.  

I'm slightly struggling with the reduction from Subset-Sum to 2-Subset-Sum, as simply adding to the set the double of each number and using the same T does not work, e.g S = {1,7,8,5} and S'={1,2,5,10,7,8,14,16} with T = 10 wouldn't work, as S' would return "true" and S should return "false".

Thank you.
There is a trivial reduction from Partition to your problem: given an instance $S$ of partition, construct the instance $(S,\frac{1}{2} \sum_{i \in S} i)$ of your problem. This shows that if you take any reduction from Subset-Sum to Partition, you immediately get a reduction from Subset-Sum to your problem. You can find the reduction from Subset-Sum to Partition in many places, or come up with it on your own.