Need help in mapping logic ...!!!

Hi Experts ,

This is with regard to my Mapping  logic i need some help in hear .

I need to have Delivery date always in interval between Start date = (Current Date +1 ) and End Date = (Current date+ 7) .

Here Current date would be the date on which PI Receives the Idoc .

For Example if idoc creation date is 20130616(yyyMMdd) then Delivery date should start with date 20130617 (Monday) and End with 20130622 (Sunday) for a Particular customer .

Can i achieve this above logic through Graphical mapping ?... Though i feel like its not possible . I Think Writing an UDF Would make sense .

Experts please do help me to complete this logic ...

Regards

Aziz khan .