Hi,

Old question, but figured I'd give an answer still.

I've done this by first inheriting the _prepare_report_line() function from report.stock.report_product_product_replenishment (AbstractModel). You can do this like:

def _prepare_report_line(self, quantity, move_out=None, move_in=None, replenishment_filled=True, product=False, reservation=False):
    res = super(ReplenishmentReportInherit, self)._prepare_report_line(quantity, move_out, move_in,
                                                                       replenishment_filled, product,       reservation)

Then, you can add the necessary data into the "res" variable and return the "res", like:

res['SOME_NAME'] = 'YOUR VARIABLE DATA'

When you've done this, you'll have to inherit the forecast-report template in an XML file, and insert your variable into the table header and body

template id="report_stock_forecasted_inh_shipped" inherit_id="stock.report_product_product_replenishment">
xpath expr="//table[@class='o_report_replenishment table table-bordered']/thead/tr/td[3]" position="after">
td>SOME NAME
/xpath>
xpath expr="//table[@class='o_report_replenishment table table-bordered']/tbody/tr[2]/td[3]" position="after">
td t-esc="line['SOME_NAME'] or ''"/>
/xpath>

Hope this helps!