If you install InvSee++_Give next to InvSee++ you will get access to the /invgive and /endergive commands. They work exactly like you'd expect:

• /invgive <player> <item type> <amount>? <nbt tag>? - Adds items to the inventory of an (offline) player. Permission: invseeplusplus.give.inventory
  
• /endergive <player> <item type> <amount>? <nbt tag>? - Adds items to the enderchest of an (offline) player. Permission:
  invseeplusplus.give.enderchest

More permissions:

• invseeplusplus.give.* provides both invseeplusplus.give.inventory and invseeplusplus.enderchest
• invseeplusplus.* now also provides invseeplusplus.give.*

Other changes in this release:

• Fixed MainSpectatorInventory#addItem, MainSpectatorInventory#firstEmpty and MainSpectatorInventory#first (both overloads)
• Fixed MainSpectatorInventory#get/setStorageContents