You can using something like:
const a = "Ef8zMzMzMzMzMzMzMzMzMzMzMzMzMzMzMzMzMzMzMzMzM0vF"a
You need to create a function which returns a splice. Something like this
slice fun_name() asm “x{0055bb} PUSHSLICE”
and then execute a function when you need a slice:
.store_slice(fun_name())
For more information, can check here
https://ton.org/docs/develop/func/literals_identifiers