The advice here regarding ACS is spot on,my question goes to the roots, my opinion is that if he's already with a good RGI then he's made the best possible leap, if the RGI is good and growing his/her business then he/she would surely be happy to sponsor the SIL when they feel the SIL is ready? Especially if the SIL is willing to put in the extra evenings and undertake day release.
The industry is designed to be hard to get into, if you are not already an RGI you really need to know one. My advice is get the SIL to sit down with his RGI and explain what he wants to do and where he wants to go, he may loose some money because he's not grafting for a day or two in the week whilst at college, but the RGI (it he/she isn't not just out for some cheap help) will respect and boulster the lad and make a path to getting registered much smoother.
The small company I work for has put through 2 young adults now who were looking for careers over jobs, 1 has stayed with us and is a real asset, the other has moved on to his own things, but in saying that, we've had probably 10-12 young guys come through and end up being labour because they just don't have the drive themselves and as my old boss used to say, if you don't ask, you don't get.
Best of luck with him, but I personally feel it has to come from him, if he wants it, has a good work ethic and shows where he wants to be, it's possible.