Assembling all transcripts for an individual gene? (using single sequence to seed the assembly)

Let’s say I have a candidate gene and I believe that in an individual sample, the genome sequence differs from the reference which then interferes with alignment.

Is there a way for me to do a “transcriptome assembly” with a specific read or sequence as a starting point? And only do the k-mer assembly from that single sequence?

I could probably code something myself but I feel like a tool to do this must already exist?

The goal here is to avoid the significant overhead of assembling a whole transcriptome when I’m only interested in one gene.