Hi @jamesmorgan,
My understanding of your use case is that addresses who can mint tokens should be also able to use the GSN.
If you are creating a new token, then you could create a Custom strategy to check in acceptRelayedCall if the from address had the minterRole and if so approve the relayed call, otherwise reject.
If you are creating a contract that has the minter role for your token, then you could add a WhitelistedRole and check that addresses were whitelisted to call the mint functionality and also in acceptRelayedCall to check the from address was whitelisted.
GSNRecipientSignature uses an off-chain service signing (using a single trusted signer) the relayed call parameters of the users making calls via the GSN to the recipient contract. In your case this would result in an off-chain check that addresses were whitelisted to use the GSN and an on-chain check that addresses were allowed to mint.
As an aside, assuming that the users who can mint are using MetaMask, then you can create a dapp that uses MetaMask for addresses to sign a relayed call: