I think we've exhausted all investment options except a likely silly bet at the bookies. When I look back at ours attending university I cringe that no grants were available to us because our income was barely over the limit. If you're a high earner the grant makes little difference to you.
Here's my tuppence worth (if I were in the same boat again):-
1. In the years leading up to leaving their secondary education I'd work my butt off with overtime (if available). I'd cut down on expenses including heating, food, petrol etc. I'd amass as much money as I possibly could before the college year was started (or even the year before). If. necessary I'd take on a part time job. I'd set up the "college" fund and try not to withdraw from it even if it were stuffing money in a mattress.
2. If I could in the income assessment year I'd reduce my working hours (and possibly the hours of Mrs Lep) to ensure our income would be under the grant regulations limit. A career break might be a good option. These might not be an option to you for various reasons.
3. My last resort (and under duress) would be to remortgage, but for some it can be a viable route. If the banks weren't co-operating the Credit Union would.
4. I get the feeling OP will not pay too much attention to the options suggested, but many looking in will because sooner or later the college nettle will have to be grasped.
I could write more from personal experiences on the matter, but won't. And if I may add a little humour to the most famous lie in Ireland "Some Day Dad, I'll pay you back . . . " takes on a whole new meaning.