Hi,
Is is possible to use the new option to activate the "Bill from task" function, in the project configuration, which allows you to add products directly to Tasks.
In the purchase order, you can select the "Analytic account" by order line ( activable to the right of the subtotal), and then only add the quantities in the purchase order line used in the given project.
Note that the product will only appear as "Other costs" in the Project/Analytic account after the confirmation and posting of the order and only if in the product configuration > Sales > Re-Invoice Expenses is selected "At cost" or "Sales price".
Only products configured as "storable product" will be reflected in the inventory.
BR
Ricardo