What are our options in Solidworks to account for the missing mass effect on a response spectrum analysis?

Suppose I have an assembly with only one significant vibration mode (lets assume its a 1DOF for this discussion) with a mass participation of 50% at 30Hz and one other mode at 150Hz with mass participation of the remaining 50%. However, lets assume our response spectrum analysis cutoff frequency is 33Hz as typical. I am I correct in believing common practice would be to apply an equivalent static load using the remaining 50% mass on the assembly, possibly simply by modeling a 0.5g gravity load? If we were to do this, what are our options to superimpose this load on the response spectrum results? Is that even valid?

Thank you.

"our response spectrum cutoff is at 33hz"

are you thinking that means that the software won't use the 150Hz response?