Put local variables for Block in a variable

This could be another case for the injector pattern:

var = Hold@{x = 2, y = 3, z = 4}

var /. Hold[inj_] :> Block[inj, x*y*z]

(*24*)
?x
(*Global`x --- so we did not leak*)

Here's something I found:

With[{h := {x = 7, y = 8}},
 Block[h, x y]]

56

The way I prefer is

var := {x = 2, y = 3, z = 4}
ReleaseHold[Hold[Block[var, x*y*z]] /. OwnValues[var]]
x

-> 24

-> x

Or

Apply[Block, Hold[var, x*y*z] /. OwnValues[var]]
x

-> 24

-> x

For

hVars = Hold[{x = 2, y = 3, z = 4}];

We can do

ReleaseHold[Hold[Block][hVars, Hold[x*y*z]]]
x

-> 24

-> x