Can't speak for Western Europe, but I would imagine it's close to Canada. Two big hurdles:
1.) He needs to prove financial means to support himself. Not sure about Europe, but for Canada, this means money in his bank account. Having a sponsor who promises to take care of you helps, but isn't enough. The government needs to know even if things don't go as planned, he can still financially support himself if he ends up alone. Thankfully this isn't a problem for me as I'd have no problem entrusting Leo with $15k in his bank account, but for others it may be an issue.
2.) You need to make the government believe he's going to return to his home country, so he has to show he has a life to return to. Sucking foreigners dicks in the upstairs short-time room of a go-go bar for $50 isn't really much of a reason to return, so you might be screwed there. This is also the main difficulty in getting Leo a visitor VISA. He has no home, car, kids, nothing. He's got about $2000 in his account, and some 40 baht/hour job. Not much of a reason to return.
Sounds like you're just looking to bring them over for a quick vacation, right? So I'm guessing a stufy VISA is out, but that's a good way to get them in, at least in Canada. Probably of no use to you, but might be to others, s:
https://accuplacerpractice.collegeboard.org/login
Practice entrance exams that mainly test English and math skills, and sound as though they're used by many colleges throughout North America. Leo and myself are looking into that, maybe move to Canmore and he can study at Bow Valley, which would be perfect for us. Beautiful small town in the mountains, and Bow Valley is basically an immigrant college -- teaches advanced English, and the necessary high school courses to get him a Canadian high school diploma, so he can go on to college / university in Canada.
I think you're going to have a rough time getting someone in under a tourist VISA though, but good luck!