Got it, then I think you have three possible ways:
• Try if a Transfer Order work with that bundle: it may be easy but the downside is that it ask you to do more steps than an Inventory Transfer (a fulfillment and a receipt)
• If you have purchased the Advanced Inventory add-on module, you can enable the Inventory Statuses (Enable Features -> Items & Inventory -> Inventory), in that case if the transfer quantity is less than the on hand quantity it would automatically set the default inventory status, otherwise it would ask to confirm the inventory status throwing an error if you’re trying to select a quantity higher than the on hand
• You can set-up a workflow that work on the items sublist and is triggered in Inventory Transfer transactions that will throw an error whenever a condition is met (e.g. with a custom formula that the quantity is bigger than the on hand quantity (both at line level)
In your position, I’d start with evaluation if a Transfer Order can be used instead of an Inventory Transfer (but I understand that the additional steps could be not acceptable), otherwise if your company’s environment have the Advanced Inventory purchased I’d try the Inventory Statuses in the Sandbox and letting the custom workflow as the last option, if none of the two above can be used 🙂