There are some people that have taken an in-line board like the Church Tx-44 super board and converted it into a make-shift mast and ski setup. I'm not sure that is the way to go in your case. I'd recommend just saving up and either purchasing a new/used mast/ski system or G2 down the line.
I use the willis knot. It takes a bit to get use to it at first. One tip is to cut the mono at an angle. The knot works like Chinese fingercuffs and I've never had it fail. The knot profile is relatively small and goes through my reel and rod guides without issues.Just make sure the mono is touching the lead in the sheath and then drag the overhand knot down so you are in essence cinching it on the backing. Here's a link that explains it better than I do.
http://www.upangler.com/leadcore.html
You definitely can flatline mono with an in-line planer board. Should work great at ice out. Just keep in mind you're not achieving any depth with this setup.
As with a lot of this stuff, there are more than one way to skin a cat. Up to you if you want to go with the lead, mono, lead, mono setup. I don't, but a lot of successful fishermen do. Good Luck!
I never used inlines. Never appealed to me and I went out of my way to create my own setup. I have a big jon setup now but this setup worked just as good and my brother still uses my old setup with equal success.
Parts lits: 1x6x8 pc of cedar ($10), orange paint ($2), aluminum post $ needed hardware ($30), clothes pins and rings $5. Reels are just old oversized spools from fishing line.
The only experience I have is with the Big John Otter Boats and they are super, can run multiple lines off each side. Last year I switched to G2's.
The G2 Planers will catch more fish than Otter Boats hands down, bit more expensive than Otter Boats, 170.00/each retail vs 100.00. So if your not on a budget, go with G2's.