FI object bitwise assignment

What is the best way to perform a bitwise assignment on a fi object? For example if i have a fi object defined as

Yfi = fi(0,0,12,0);

and another smaller fi object defined as:

Zfi = fi(0,0,4,0)

and i wanted to assign bits 8:4 of Yfi with Zfi how should i go about doing it:

ideally i would like to be able to do it this way:

Yfi(8:4) = Zfi

but this doesn't seem to work.

I know i could play games and do something like this:

R = bitconcat(Yfi.bitsliceget(12,9),Zfi,Yfi.bitsliceget(3,1))

but it seems there should be and easyer way to do this.