A generalization of Rao's theorem to graded $R$-subalgebras of $R[t]$

Let $R$ be a Noetherian local ring of Krull dimension $d$ such that $(d!)R=R$, and let $A$ be a graded $R$-subalgebra of the polynomial algebra $R[t]$. We prove that every unimodular row of length $d+1$ over $A$ can be completed to an invertible matrix. This is a generalization of a classical result by Rao, who proved that in the same setting, every unimodular row of length $d+1$ over $R[t]$ admits a completion to an invertible matrix.