I heard making your Tulpa read could help, like, as if (half-)parroting them.
We haven't tried yet because most of what we're reading throughout the day is in English which isn't our native language and emulating the accent is too distracting. Once we find something worthwhile to read in our native or that other language we've been learning we'll be trying this. Speaking of languages, if some of you are learning another one, make your Tulpa participate, involve them, make them help.
In our case, on this particular topic, I won't go into details but I believe I'm mostly at fault, like I'm unconsciously holding my Tulpa back. With that said we're still making progress, as slow as it is. I think it's important to keep in mind that it's somewhat hard to gauge the progress of a Tulpa you're sharing life with. For those who've had younger siblings (or children), it's like a baby or a kid you're living with, you're don't exactly realize they're growing, if that makes sense.