Is it possible to have a custom look-up table to map ids to other ids in the configuration file?

E.G.

TestLookValues

key | value

1 |100

2 | 100

3 | 600

lookup("TestLookValues", "3")

gives $var(lookupval) equal to 600

It is similar to MTree functionality only I am looking for an exact match not just a prefix

TestLookValues

prefix | value

1 |100

2 | 100

3 | 600

mt_match("TestLookValues", "3003)", "0")

gives $var(mtval) = 600

I would need $var(mtval) = -1 (not found)

Thanks Gareth