I posted a suggestion on r/nanocurrency an they told me that this forum would be more appropriate for post like this.
In the case that the Ledger pruning become reality this idea may mitigate the Ledger bloat problem, in particular it aims to solve the Penny Spend Attack.
In practice, each wallet must be coupled by a value (nonce) that satisfies:
hash(address + nonce) = [N BIT TO 0] [REMAINING HASH]
where hash is a ASIC resistant, GPU proof hasing function; N is the difficulty.
The difficulty could be set to a value that about 1h is needed to find a valid nonce: to create a wallet you need to dedicate a CPU for one hour to this task. Once the nonce has been found the wallet is ready to send and receive Nano. (1h is totally arbitrary I don't know if it can be a reasonable time)
To send Nano from wallet A to wallet B the sender must also provide the nonce of A and B or the transaction will be rejected. When a receving address is shared (for example through the QR code) the nonce must be included or the sender will need to find a valid nonce for the wallet (computationally expensive).
An attacker who wants to make the ledger bloat would have to create hundreds of thousands of wallets, with an absurd computational cost.
Another suggestion derived from the comment below says that could be more convenient to increase the already present PoW difficulty only for sending Nano to not opened accounts.