I've not tried doing this with glass, but ice works IIRC, and any solid block or slab will work… (white wool will look somewhat like a permanent cloud, light blue blends fairly well with the sky color).
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WARNING: I have an extemely "grindy" playstyle; YMMV — if this doesn't seem fun to you, mine what you can from it & bin the rest.
You can use some kind of hidden lighting method. You don't necessarily need torches to be all around your pond to keep it from freezing, you just need some kind of light source. Try doing a google search for hidden lighting methods. Or just add glowstone to the bottom of your lake.
You could also try using a third-party world editing software to change the biome. However if you don't have any experience with this kind of stuff then it would probably take longer than just adding lighting in-game.