However, I'm in the middle of a cash-out refinance of an investment property I already own.

Use the HELOC on cash-generating opportunities like flips, then use the cash generated to buy long-term buy and hold investments. 

Acquiring in cash or with a fix and flip loan.

Positive Cash FlowImmediate cash flow isn’t always possible in growth markets.

But the GP made there money setting the deal up front and not so much thru the end cycle.  

Quote from @Daniel Tanasa: Another option is to get a small cash out refinance from the house you plan on fixing up, if is in financeable condition, and use that to fix it up, while still cash flowing.

Many will provided exaggerated numbers or omit information up front. 

We have done it both ways where we fund purchase and they cover rehab but if the individual is less experienced we do not do it that way, we have them put more money into the deal from the start and fund the draws, reason why is we also had a deal where the person said they would do this and never did anything and property sat and loan matured and it was a pain.Just recognize you will still not get 100% financing for the purchase, so you are putting money in up front. 

If you don't have appreciation capex will wipe out your cash flow. 

@Christopher Alley we use a lot of private money in the rehab business, and I have never paid any up front fees.