If you're using Design Studio to create your ProcessFlow Inbasket displays, you aren't limited to a Formlet, you can use a Data Query.

Here's how to include select criteria from the variables in your flow so that only the data you want will be displayed:

function data0_OnInit()
// create new variables and reference the variables from your flow (page.parameters.FLOWVARIABLE)
var myVen=page.parameters.VEN
var myInv=page.parameters.INV
var myItem=page.parameters.ITEM

// data0 = your Data Query name
var dmeObj = page.objects["data0"];

// pass your variables as Select criteria to your Data Query
dmeObj.criteria += "SELECT=VENDOR%3D" + myVen + "%26INVOICE^%3D" + myInv + "%26ITEM^%3D" + myItem