If you simply need to create a rotation value based on scalar values, you can use the Make Vector node (found in the Tools section) to send a single value to a specific channel. To convert scalar values (especially 0-1 ranges) to known angles (say, 20°), I usually multiply a Scalar value with an Angle node (in the Constant section).
To clarify, the Vector node labels the three channels as X/Y/Z, but they're equally applicable to H/P/B. Lightwave is actually really great at combining or converting between different types of data. For example, if you plug a scalar into a vector or colour input, you'll just get greyscale values (X/Y/Z or R/G/B channels are all set to the same Scaler value input).