Looks like you are working on standalone MS Project(since you mentioned you don't have SharePoint) and not in project server connected mode, if that assumption is corrects, then i have to say there is no OOB way to do so, however there are
workarounds and 3rd party tools available which can do it for you
We have an excellent post by Ben
here on how to perform this workaround which is a combination of excel and macro
Also you can look at 3rd party tools like Allocatus, easyprojectplan.com, easytasksync.com etc..
Thanks | Sunil Kr Singh | http://epmxperts.wordpress.com