Hey there, so far, I haven't found any software that does what you're looking for. The only way right now (that I know of) is to add people manually. Yes, you'll be the one viewing their profiles and clicking the add button. It takes time and effort but in the end, you'll be adding those that you really want to add and the results will be a lot better than an automated one.
If you don't want to do that, then you can just simply hire somebody else to do it for you. You'll give that person the authority to manage your account and to add lots and lots of people.
I'll let you know of ever I come across a software of something of the sort.
