Lock SAP transactions using WebDynpro

I have a requirement in my project where I need to lock SAP standard transaction for a document number if the same is under process from portal (webdynpro).

We have standard transactions like VL02N where we can enter a document number for processing. Now if we try to process the same document number from portal, it gives message that document number XXXXX has being locked by user XYZ.

We want a vise versa scenario to be incorporated from WebDynpro. I mean if the document number is under process from portal, SAP transaction should get a message that the document number has been locked by portal.

Are there anyways to incorporate this? If yes, could someone please throw light on pros and cons of these kinds of implementations (I mean performance vise or feasibility vise).

Ashutosh Moharir