Timesheet Tasks in Zoho Books: associate to service item

Timesheet Tasks in Zoho Books: associate to service item

How do we associate a service item to timesheet tasks in Zoho Books? For example: Joe spent 5 hours on project:task1 which is Service Item#1 (Income:Service1). When the invoice is issued thru the Project Invoice section, this is not available. When the invoice is issued thru Sales section and we bring in the time to be billed, it shows up as a second section from the Service Item. Any hints or assistance appreciated, been trying to get this nailed down for several months and need to start sending clients invoices directly from Zoho (vs. offline). Thanks!