You can turn off having PDM control the rev block. Run SW Workgroup Vault Admin, go to the Revision Table tab and de-select "enable rev table". This will take away some important functionality in PDM but it will help with the chicken/egg scenario.
If you add the revision that is going to be applied to the revision table prior to checking in you can place your symbols. When you come to check the file in you can add the note. The revision table will retain your applied revision letter or number and add the note you applied at check in all of your symbols will remain on the drawing.