That sounds like a very plausible work around. Certainly lower maintenance than constant bank transfers but I kind of like tying the stipend to the whole vassal/liege agreement.
That being said, this has some seriously cool potential. Set up Different ranks with different funding levels. One level grants 100G, the next 75G, 50G, 25G and so on. Have each knight of the realm who needs the boost join and get assigned to the appropriate level based on how much money the need to maintain a decent unit. Sponsors just keep pumping money into it.
This could even make it possible to pay knights to serve and fight even without a lord or estate (hedge knights). A lot of fun potential here!
