There is now a Chrome extension in development (1.1 released) that lets you sync your account balances from YNAB to PL to save you the trouble.

What's ProjectionLab you ask? It's a natural planning successor to YNAB. Once you have your current house in order it's time to start planning for the future and PL is awesome at it.

I have no affiliation other than a very happy user. The dev of PL is very responsive on Discord as is the extension dev.