I looked into the feasibility of this a while back. It's possible, but requires that you get even more abstract than Epic is already.
Troops work fine—just use one infantry model to represent a stand of that type (eg Marine with a bolter = Tactical, Marine with a jump pack = Assault, Marin with a heavy weapon = Devastator, and so on).
Vehicles are more of a problem, for two reasons. One: you'll never have enough 40K models for a 1:1 representation. Two: the vehicle sizes mean that having a 1:1 ratio (so, a Tatical formation with six stands and three Rhinos actually has three Rhino models) just looks crap.
Your best bet, I reckon, is to either buy Epic vehicles or to abstract vehicle use.
To abstract the Tactical formation, for example, you would take just one Rhino instead of three, make it DC3 warengine (so can take three hits without being destroyed), and then apply a rule that each DC casualty suffered also destroys two carried stands. You would have to be careful how you applied the warengine rules, but it would generally work.
Ditto with things like Land Raiders. Treat the one model as four Land Raiders by giving it DC4. In the case of shooting units, like a Land Raider, though, you would then also need to apply a multplier to its shooting based on its remaining DC. For example, a Land Raider unit shoots 2xAT4+ lascannons and 1xAP4+ heavy bolter. If your Land Raider formation has just 3 of its original 4DC remaining, you would multiply these weapons by 3. In the example above, this would mean the unit shoots 6xAT4+ lascannons and 3xAP4+ heavy bolter. Doing this will keep the single model en par with a formation of four units.
Hope that helps. It won't be perfect, but it should enable a decent, lower-points game (say, 2,000pts).
Good luck, and enjoy!