So I had another brainstorm...
Problem:
Now that we've thrown printed LA's out the window and are using creatures with fractional CR's, how do we decide how much XP troops need before they level?
Intermediate Info:
The formula used in the DMG is

*(n-1)*500xp.
i.e. Level 3 = (3)*(2)*500xp=3000xp
Lightbulb:
This works just fine with fractional levels.
Example1:
My general is CR 13.3. With a PC level being equivalent to .8 that makes him level 16.62.
His current XP is (16.62)*(15.62)*500=129,841xp
To add a PC level he needs to reach (17.62)*(16.62)*500 = 146,422xp
(Note: Per Fieari, current XP is actually half-way between those values)
Example2:
My crossbowmen are CR .66 (level .825)
Current = (.825)*(1)*500 = 412xp
(Zombie Kobold)
Next Level = (1.625)*(1)*500= 812xp
(Zombie Kobold Ftr1)
Add another level = (2.425)*(1.425)*500=1727xp
(Zombie Kobold Ftr2)
Negative values didn't make sense and neither did squaring low values, so I capped the second value at 1.
It's a little wierd for low-CR troops at low-levels but it effectively works. (i.e. zombie kobolds are pretty worthless, so they effectively have a negative LA)