Possibility to limit purchases?

Just wondering if anyone knows if its possible to make say onetime purchaseable items/commands?

Example: Backpacks plugin in conjunction with backpacks upgrade plugin allow you to use the command bpupgrade to increase the storage of the backpack to a maximum of 7 rows, im able to implement the upgrade in the store fine however i can see no way of limitting the times this command can be purchased as anything past 7 uses takes the RP but gives no upgrade due to the backpacks limitations.

The only way i can 'limit' it to an extent is by making multiple purchase options and adding a cooldown of say 99999999 to prevent them from buying that item for the duration of that cooldown however this then adds the ugliness of upon clicking to purchase that item/command again it just states 'you have X time remaining on cooldown' etc

Any help would be great 

Interested in doing this as my 1st mod, checking with k1llyou if it's ok for him. Wouldn't it better if you had one option for each row and it offer the correct one based on how many you got ?