How to add "Virama" to mute vowels associated with consonents?

[akashiii]

When I try to transliterate Sanskrit text (NabhaH Sparsham Deeptam) to
Devanagari I get this: नभः स्पर्शम दीप्तम.

When I try edit text to force the the consonent with a "virama" to
mute the vowel (it looks like a little slanted line under the
consonent), the transliterator lets me do this in the keyboard mode
but refuses to accept the change in the text field.

For example: In the word स्पर्शम (Transliteration: "sparshama"), I'm
try to get the sound "sparsham" by muting the consonent associated
with the consonent "म" (for which one needs to include a virama under
the consonent "म")

Is there any way one can do this?