Mmh, it might be really hard.
The problem with Dominix is the fact that your DPS is almost only composed of Drones, even if you strap some large railguns on it, because the hull doesn’t have bonus to hybrid weapons your DPS will stay quite low.
The improved AI of sleeper drones make it a tough job for drone users, as the “threat” level used by the defending rats will generally point the main damage sources as the biggest danger, compared to two battleships remote-repairing each other, but having low to no damage output. Even more, a battleship is generally not enough to generate enough threat level to keep the drones safe.
Concerning your idea of two spider-tanked Dominixes, The sites are probably going to take forever to complete, and you don’t want to stay in a site where you can directly be warped to for too long in wormhole space. Sadly, two Rattlesnakes might be your best bet.
The training time will not be a problem, as you should already have good drone skills, and the hull require the skills for Gallente and Caldari battleships, so you already have one. I’d say you’ll just have to train for three days and you’ll have the skills for a Rattlesnake. Concerning cruise missiles, might be problematic here, but it’s your choice. You can train them or not.
The tactics with Rattlesnake will be a bit different. When you spot a combat site you are willing to run in the C4, warp in at extreme range and deploy sentries. As they will be extremely far from the drones, they shouldn’t take damage. And if they do, you can recall them immedialty if you stay near them (don’t move then). With the 'Snake bonuses, your sentries will tear appart small ship that burn toward you at low transversal, so pick frigates and cruisers (in that order) before trying to pierce the hull of sleeper battleships.
If the drones start to get closer, you could either swap your sentry drones for heavy drones (with some Omnitracking computers loaded with the tracking speed script, they should be able to track cruisers. Don’t try on frigates) and attack the ships that are too close for sentries, or use a Large Micro Jump Drive (LMJD) to get 100km away from them and continue the snipe. This also mean you’ll have to get used to the use of this module to not end up in the middle of the enemies. And because C4 sites start the have warps scrambling ship, you won’t be able to escape.
Here, with twin Rattlesnakes, you should be good. However, if the heavy RR present in the site is too much for you, try to get a third character in a Scorpion with heavy tank to break the chain.