Beta for Inv Firm

I wondering if anyone has run into this. I'm trying to come up with a WACC for an investment management firm and to do this I need a value for beta.

The approaches I could think of are:
1. Use an industry average of comparable publicly-traded firm betas
2. Use some asset value-weighted beta of the firm's underlying funds for which betas are available. I have betas for most but not all of their AUM. (of course in some instances you might not have this data)
3. Beta = 1 (does this make sense even if the firm manages all Eq or all F/I, or some non-correlated asset?
4. Other?

thanks.