My Cars: 2007 Citroen Xsara Picasso 1.6 16V VTX 1982 Citroen GSA Spécial Estate - gone to a new home 1991 Citroen BX16 TGS Meteor - still out there somewhere!
I had a thought: I wonder if plasticine would make a good masking material? Stick it around and inside the lettering, use a small roller to compress it and make a flat surface - then remove it all once the paint's dried... might be a bit less fiddly than cutting up small pieces of masking tape.