I'm not sure if that's possible, but given that very specific error message, it looks like it's not. I'm running a bit of a mix of that and the 40g ports on my home stack, it's stacked via a trunk of 1 40g port and 1 breakout port, leaving me 2x 40gbE ports and 2x breakout ports
it's also worth noting stack traffic over the 4x 10gbE QSFP+ ports is hashed similar to standard LACP, eg by source IP / port. Meaning if you stack using only the breakout ports, you won't get single-stream speed above 10gbps between stuff connected to each stack member. so 40gbE host on switch 1 is not going to be able to do more than 10gbps for single stream stuff (eg something using only one source IP and one source port, like SMB shares etc (unless running SMB 3.0)) to a 40gbE device on switch 2, as it will get hashed to just 1 of the 10gbps stacking channels