Attach a signed internal memo to support a signature request

I have a contract to be signed between my organisation and a vendor. The person from my organisation with the authority to execute the contract has not been directly involved in the contract negotiations and will know little about it. 

In order for the approver to sign, they need endorsements from with my organistion. On paper this is achevied via an internal memo, with endorsemens (signatures) of senior members of my organisation who the state they support the signing of the contract. This gives approver the confidence to sign.

How to achive this in the Adobe Sign world? I can create a memo to obtain the chain of internal  signatures digitally, but this memo must not be included in the contract sent to the vendor. I can't therefore simply include all internal approvers and the vendor in the workflow becuase the vendor will see the memo in addition to the contract.

Any ideas on how best to handle this scenario?