NBitcoin get signature, use spending P2SH transaction with non-standard script

After creating a new NBitcoin transaction (with a single pay-to-script hash input and multiple outputs), is there any way to calculate the transaction signature and manually put it in the inputs[0].ScriptSig, along with other parameters used by the script?

A related issue is whether (and how) non-standard scripts can be used in P2SH transactions.