It depends somewhat on your setup. Are you encrypting a file, then mailing the encrypted file to the recipients, along with a plain-text email? If so, you could potentially add all of the keys to the file when you encrypt it as a PGP zip.
If you are encrypting files to the same set of people every time, you could potentially add their public keys to Tools>Options>Master Keys. If you do this, any files you encrypt will automatically have the Master Keys added when you encrypt. You would simply right-click the file and select "Encrypt to Master Keys". This could potentially be unsafe if you wind up encrypting files to keys that were unintended because the key was not removed from Master Keys before a file was encrypted.