Yes, it is possible to track the expenses on a potential project for a potential client so that if the project or job is won, you can convert the time and expenses spent on that to billable.
In this case, you can create a new project and set the contract type to 'Marketing' and associate a budget or estimate to it as well. Record any time spent on this project or any expenses incurred on it. When the project is won, change the contract type from 'Marketing' to a different contract type, such as 'Fixed Fee' or 'Hourly.' Core asks if you would like to convert the logged time (non-billable) to billable time. Select 'Yes.'