re-using each vertex from second vbuffer n times

I basically have two vertex streams / VertexBuffer objects and want to draw using both of them - but only advance the second stream for every nth element of the first - or in other words: I want to ‘spread out’ the second vbuffer to the length of the first. I couldn’t find anything online, but tbh im not even sure if it’s possible. I could ofc just put each value in 3 times, but that obviously wouldn’t be very efficient.
quick example:
vb0:[0, 1, 2, 3, 4, 5, 6, …
vb1:[0, 0, 0, 1, 1, 1, 2, …

afaik as long as you don’t do hardwareinstancing, multiple vertexbuffers are fed sequentially to the shader - but maybe you can use hardwareinstancing one way or the other

Anyway, even if what you want to do is possible, as the GPU makes a lot of use of data caching and readahead, just having your values multiple times in the buffer is most likely more efficient than working with a non-1 stride

its not like i cant get two buffers into one shader, ist just that every element of the second buffer should be used for multiple elements of the first