I tried the following approaches, but none of them seemed to work:

H 20 * * * %SOMEMULTILINEPARAMETER=valueA\nvalueB

H 20 * * * %SOMEMULTILINEPARAMETER=valueA,valueB

H 20 * * * %SOMEMULTILINEPARAMETER=valueA
nvalueB

In all cases, what is placed to the right of the equal sign is directly translated to the parameter's value, and thus the Jenkins pipeline fails, as it is expecting a multi-line string value