Play a Short Battalion as Easily as a Lance

Provided that you're not too keen on 1:1 accuracy with the fictional setting, there is a very simple way to preserve the "feel" of BattleTech while fielding seven times as many miniatures:

Assign each location on regular 'Mech sheets to a separate figure.

Ignoring the head, this turns a lance into four squads of seven (twenty-eight figures total), and uses basically all the same rules as regular BattleTech. No need to roll on the hit location table, obviously, since each figure will target other figures individually; jump jets apply only to whichever figure has 'em on its crit table; heat is shared across all units in the squad; use 60-degree firing arcs, no rotation, for all figures; critical hits largely the same, except shoulder/hip crits immobilize the corresponding figure; figures occupy the entirety of whichever hex they're in, and can block LOS; ammo explosions apply full damage to the hex they're in, then apply half the excess to adjacent hexes; limbs mass 10% of the "full" 'Mech's mass and torsos mass 20%; physical attacks and weapons attacks are handled in the same phase, since each figure can only do one or the other anyways; each figure can do whatever physical attacks the location could normally, except that torso locations do 1/3rd normal charging damage.

Variations:

1. Instead of making a second roll to check for critical hits, treat a roll of doubles on any appropriate To-Hit roll as a single successful crit.
2. A squad deactivates when its "Center" is destroyed.
3. Jump MP replaces ground MP 1:1 instead of being a separate movement mode.
4. "Leg" figures can move anywhere they could normally; torsos can only move towards "legs," and cannot move beyond legs; arms must also move towards legs but can also continue beyond them.
5. Split-location equipment (ammo, autocannon spillover crits, Artemis, etc) is removed from its current location and considered to be mounted outside the armor on the rear hexside of whichever figure carries the primary/bulk of the associated weapon.
6. Legs get zero free facing changes; torsos get one free facing change; arms get two free facing changes.
7. Figures (for purpose of city fighting or physical attack damage) determine their mass by summing all equipment and armor and structure etc. in the location. Assume split-location equipment spreads mass evenly across all crits, and that the engine puts 1/3rd of its mass in the center torso and splits the remaining 2/3rd between the legs.
8. The "Center" figure absorbs the head location's armor & structure and weapons, but ignores pilot effects. 
9. Instead of the "short/medium/long" "+0/+2/+4" brackets & modifiers applying to the range between shooter and target, assume all weapons are always in range, and apply them instead to the target's movement in place of the standard Target Movement Modifier table. Green pilots subtract one hex from their effective movement for this purpose; veteran pilots add one. 

Edit, November 16, 2012:

• Alternate to variations 2 & 4: the center must remain within (Flank MP) hexes of at least one leg; each side torso must remain within (Flank MP) hexes of the center (or the hex the center was destroyed in); each arm must remain within (Flank MP) hexes of the associated side torso (or the hex the side was destroyed in).
• Alternate to variation 8: each item in the head gets assigned to different non-center location; when a non-center location is destroyed, the whole team suffers effects as though the corresponding head item had suffered a critical hit. 

Edit, August 1, 2019:

• Don't know when this dates to, but I just found an old note suggesting that each unit track heat individually and units in base contact can share cooling capacity. (Harsh.) Possibly as an alternative to the movement restrictions mentioned earlier.