Reg O says,
"(c) A member bank is authorized to extend credit to any executive officer of the bank:
(1) In any amount to finance the education of the executive officer's children;
(2) In any amount to finance or refinance the purchase, construction, maintenance, or improvement of a residence of the executive officer, provided:
(i) The extension of credit is secured by a first lien on the residence and the residence is owned (or expected to be owned after the extension of credit) by the executive officer;"
You could loan additional money to the exec for improvement, but since it has to be on a first lien, you'd need to combine the existing HELOC and the new money into one loan secured by a first lien on his/her residence.
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Opinions my own.