Send Data To Ashx - Handler But Not Query String?

I would like to open some page from external web-application in iframe. Usualy, I would indicate URL for iframe like this: URL = [URL] BUT. I need to send not only 'ID=12' parameter. I need to send a lot of data to handler in order to be processed. Usualy I do it by following code:

Dim wrq As WebRequest = WebRequest.Create(Data_WS_URL) wrq.Method = "POST" Dim postData As String = "PubmedIDs=" & vInput wrq.ContentType = "Application/x-www-form-urlencoded" Dim byteArray As Byte() = Encoding.UTF8.GetBytes(postData)

But when you use this code - you recieve response from webrequest as some amount of data - text or binary. I may write this respone to the place on the page where I wanted to have iframe. But response cannot always be accaptable. (for example - I render asp:Treeview by ASHX handler - when I do to ashx page - it renders well, collapse-expand works fine; but if I write web-response of ashx page as text/html - then there's something wrong with javascript, tags ids and collapsing nodes). And webresponse cannot be represented as as URL. How to combine this two approaches

1) Clear URL which can be set as source for iframe
2) Extra data for web-request, larger then QueryString can handle