Passing URL report parameters directly to a report in a SharePoint Document Library is enabled in the SQL Server Reporting Services 2008 Integration with SharePoint Add-in.
Why? Key intent is to allow specifying non-default report parameter values when rendering of a report in full-page view in SharePoint.  
How do you use this feature? Simply add-on the URL report parameters onto the URL displayed in SharePoint when viewing a report in full page view. 
Examples: Here are examples using the Adventureworks sample reports assumed to be stored in SharePoint document library: http://<SharePoint_site>/Reports/ReportsLibrary
·         Render the AdventureWorks "Employee Sales Summary" report for 'Syed Abbas' for 'January' / '2004' with ReportViewer Toolbar showing pagination only: http://<SharePoint_site>/Reports/_layouts/ReportServer/RSViewerPage.aspx?rv:RelativeReportUrl=/Reports/ReportsLibrary/Employee%20Sales%20Summary.rdl&rv:ToolBar=Navigation&rp:EmpID=288&rp:ReportMonth=1&rp:ReportYear=2004
·         Render the AdventureWorks 'Product Catalog' report with the Document Map Area collapsed and no Header Area: http://<SharePoint_site>/Reports/_layouts/ReportServer/RSViewerPage.aspx?rv:RelativeReportUrl=/Reports/ReportsLibrary/Product%20Catalog.rdl&rv:HeaderArea=None&rv:DocMapMode=Collapsed
ReportViewer parameters for controlling full-page report rendering
ReportViewer Parameter
Description
Values
rv:HeaderArea
Control how the ReportViewer web part’s header is displayed in full-page view.
Full, None.
Default: Full
rv:ToolBar
Control how the ReportViewer web part’s toolbar is displayed in full-page view.
Full, Navigation, None.
Default: Full
rv:ParamMode
Control how the ReportViewer web part’s header is displayed in full-page view.
Full, Collapsed, Hidden.
Default: Full
rv:AsyncRender
Control whether the report is rendered asynchronously or synchronously.
true, false.
Default: true
rv:DocMapAreaWidth
Control the display width in pixels of the ReportViewer web part’s Document Map area.
Non-negative integer
rv:DocMapMode
Control the display of the Document Map area of a report.
Displayed, Collapsed, Hidden.
Default: Dislayed
SQL Server Reporting Services 2008 R2
In the Report Viewer that ships with the SSRS 2008 R2 Add-in for SharePoint the following new Report Viewer parameters are added:

ReportViewer Parameter
Description
Values
rv:DockToolBar
Controls whether the ReportViewer web part’s toolbar is docked to the top or bottom.
Top, Bottom.
Default: Top
rv:ToolBarItemsDisplayMode
Controls turning of or on specific parts of the ReportViewer web part’s toolbar. This is an enumeration field  eg. For no Actions menu rv:ToolBarItemsDisplayMode= 63 (or 0x3F); For all of Actions menu only rv:ToolBarItemsDisplayMode= 960 (or 0x3C0)
Back= 1, (0x1)
Find= 2, (0x2)
Page Navigation=4, (0x4)
Refresh= 8, (0x8)
Zoom= 16, (0x10)
AtomFeed= 32, (0x20)
Actions Menu Print= 64, (0x40)
Actions Menu Export= 128, (0x80)
Actions Menu ReportBuilder= 256,(0x100)
Actions Menu Subscribe = 512, (0x200)
Default: -1