I have seen it done, and should be fairly easy if you buy the right sacks. One's with top fill and a bottom drain hole. I have an 02 SANTE with the rule 1100 pumps and the hard tanks, I will probably end up adding the new PRO-X wedge sacks and plumbing them in to fill off the overflow of the tanks and drain on their own pumps. A simple 2 way valve, check valve, a couple fittings and a couple pumps could do it.
I know the tanks are fairly easy to remove as they have to be for engine repairs. all the plumbing and wiring is right there, so it's a pretty logical thing to do, you will only lose the fill gauges, (whatever!). One bit of concern is the divider between the storage compartments and the engine. The 2 piece walls are a bit flimsy and I could see a sack rolling into the wall and perhaps pushing it's way through to the engine. There are probably some fairly simple ways to either bolster the wall or add some straps to secure the bags.
The tanks are a nice, safe way for CC to add a stock ballast system with gauges. Most rider add weight anyway, so it's not a big deal to remove the rear tanks and put in what you want. you can easily do it without wrecking the system and set it aside for safe keeping.
What year is the SAN??