I'd be possible, but only if it's not raining tomorrow. Might just hack an old cat5 cable and see how it goes. Having new Cat5 would make it easier to do the pairs than the current 3-pair cable that uses the old colours.
The very fact that it was okay for a few hours without dropping, then to have it drop and sync at 6 or 7Mbps, to me, sounds more like an issue further away. Like it's resetting me to ADSL1 or something. Pass. I'm going to keep searching and see if I can find a solution.