Re UMD--
Base Charisma 16, +3 UMD
+5 UMD from four different sources, 10k gold
+4 Cha (+2 UMD), 16k gold
5 ranks on spellcraft (+2 synergy)
5 ranks on decipher script (+2 synergy)
This gives +29 total.
Assuming you are 12th level and you max your cha (+3 = +1 UMD) and your UMD skill ranks (+15) you now have +45, means you need to roll 10 or higher.
All you need is spending 1650gp on every single scroll of disintegrate (DC 10+6+15 = 31) and cross fingers that your opponent (likely being 12th level at least) doesn't have a +21 on Fort (+8 from class, +6 from con, +2 from feat and +5 from one or more items that add up) so they have a smaller chance of resisting than you casting...
EXCEPT
The scroll's DC is not set by the user's ability score; it is set by the scroll's creator and usually it's the lowest needed to scribe the scroll in the first place. (Int 16 for a level 6 spell, means DC19)
Second, the purpose of the Emulate Ability Score "task" is to fulfil minimum requirements. Is it mentioned anywhere that you can incorporate them into any computations?
E.g. when using a ranged touch scroll, can you emulate a high Dex to have an attack bonus? N.O.P.E.
When attempting to control a sphere of annihilation, can you emulate a high Int? No because it's not a prerequisite. Even if you do it does not influence your control check.
When using a +1 greatsword with your Str 5 (2d6-2), can you emulate Str 40 and deal 2d6+23 damage? Again, no.
What's more, a dwarven waraxe has a str requirement of 13 to use it one-handed. Can you emulate at least Str 13 to do so if the axe is magical? No way.
Now is the place to object before it gets into "live operation".