How can i reference a workflow variable inside JSON tool plugin

i need to add the value of a workflow variable into the JSON URL i tried using #variable.variableName# hash value but it did not work, for example my JSON URL inside the JSON tool plugin looks as:-

web/json/getdocumentinfo/documentbyid?documentid=#variable.documentid#

But using #variable.variableName# inside JSON URL is not the right approach as it will not work, so how can i solve this problem?

BR

I also tried adding something as :-

'http://localhost:8080/jw/web/json/workflow/process/view/' + #variable.imagurl# + ':35:process1?j_username=kermit&hash=9449B5ABCFA9AFDA36B801351ED3DF66&loginAs=customerservice'

but it will not work either...