Looking to pick your brains...

I've been dabbling in REI for a couple years. Have a few rental properties and have flipped a handful of SFHs. REI is not my FT profession (nor do I want it to be), but I do want to continue flipping a couple houses at a time (6-10/yr) to supplement my other income. I live in the Nashville market, and most of my experience has been with properties wholesaling for 150-200k w/ an ARV 250-300k. I enjoy flipping a couple houses at a time, but I don't want to turn it into a FT job.

My question:  I have ~$1MM cash and I'm trying to determine the best way to put it to use.  I've considered simply buying properties with that cash and avoiding financing all together, but I'm afraid that will lead to a significant portion of my cash "sitting on the sidelines" more often than it's being put to use.  

My latest idea is to put most of the cash in a relatively low-risk investment - mix of bonds and gold ETF - then take an SBLOC against that portfolio to purchase my flips with.  My reasoning - my cash can constantly be at work in the aforementioned portfolio (as opposed to a money market type of account), but I still have access to 60-70% of the cash to continue flipping a couple houses at time.  

Any thoughts from you sages?

Thanks in advance -

Daniel