Another vote for having a round white plastic rapid feeder among your collection of bee-bits.
But its not the answer to everything - and sometimes the bees may be a bit thick about realising that they need to go up, and then down to get to the syrup.
A leafy twig stuffed down the 'chimney', towards the hive, with a couple of spoonfuls of syrup dribbled over may help them find their way up.
If you can do it before there are bees involved, its a good idea to position the feeder exactly above the hole, and then mark round it on the crownboard, to show you where the feeder needs to be positioned.
This is particularly so with the 'off-centre' hole, that you will probably position directly above your mini-colony, for most effective feeding. One less thing to fuss over, when there are hundreds of bees that haven't understood what is expected of them!
For feeding really small quantities of syrup to a small colony, I've been impressed with the contact feeder 'lid' that screws onto a standard honey jar. Not for feeding honey (don't even think of it), but for feeding syrup better than the traditional 'punch a few small holes in the lid' approach.
At a couple of quid, its very well worthwhile to have available. (If the rapid feeder isn't at least half full, or they don't think its warm enough, they may not do much with it.)
The glass jar makes it really easy to see how much syrup remains, and the bees take from it very easily.
Only thing to be aware of is that its not quite big enough to cover the whole of the standard feeder hole - which is sized for a porter escape. I use a trimmed-off bit of thin clear stiffish but flexy plastic, that I think came from around a bought-in sponge cake, to cover the rest of the hole.
Good idea to order at least one of these things at the same time as your plastic rapid feeder.