The purchasing configuration tab does allow for multiple accounts and passwords to be entered, separated with a ':'.
There is a problem in that the lab need to remember which supplier account is linked to their lab account.
This is solved by using the supplier tab in the customer update screen.
This lists the lens suppliers that have multiple accounts. If there are no suppliers with multiple accounts then no lens suppliers are listed. To connect a lens supplier then select on the lens supplier and the accounts are shown.
If the setting "Automatic Add to Purchasing" has been made then when the lens supplier is chosen at the end of order entry, the selection will look at the customer record and choose the matching account for the lab supplier.
This will mean that order entry in automatic mode can process and in manual mode there is no need to try to match customer account and lens supplier account.