this is how i did the split using the gridcoinresearchd daemon on Linux. Thanks to @jamescowens and @ifoggz for further clarifying my questions.

i manage a pool of Gridcoin miners and we collectively held 25'000 GRC spread over 7-10 addresses, some with less than 300 GRC. So, after reading this article, I decided to split the 25'000 GRC on two addresses only. If one just staked, it has 16 hours to wait, but the other one will still try to stake without waiting.

assuming your wallet is unlocked, you first create two new addresses for staking by issuing the command
gridcoinresearchd getnewaddress stake1
[address1]
gridcoinresearchd getnewaddress stake2
[address2]

then do a backup of your wallet, so that you have the public and private keys that control the new addresses backed up. Just issue
gridcoinresearchd backupwallet
In subfolder .GridcoinResearch/walletbackups you will find the backup wallet.dat with a date and timestamp
This file is very important, as all your previous backups are invalidated as they do not contain the new public and private keys needed to control all your GRCs.

Once your backup is copyed to another physical location, it's time to move the gridcoins, we first move everything but a little dust (for the fee) to address 1:
gridcoinresearchd sendtoaddress [address1] 24999.9999

We can wait some time, until this first move is persisted on the blockchain. You can check
gridcoinresearchd listtransactions
and wait until you have say 3 confirmations (your transaction is buried 3 blocks down in the blockchain).

As final command issue
gridcoinresearchd sendtoaddress [address2] 12500

Following this procedure you end up with 2 addresses of 12500 GRC and one address with very little gridcoin dust.

Happy mining!